Hippolytus’ difference between hearing the Word and hearing the Gospel? In Apostolic Traditions, Hippolytus (starting at section 15 through section 20 (it is too much to copy and paste)) lines out the qualifications that a catechumen must meet for acceptance as such and a 3 year period that accepted catechumens must undergo prior to being baptized.

Accepted catechumens will hear the word for 3 years so long as they faithfully retain accepted catechumen behavior.


  Catechumens will hear the word for three years. Yet if someone is
  earnest and perseveres well in the matter, it is not the time that is
  judged, but the conduct.


Having successfully completed the catechism and been presented as baptism candidates they are allowed to hear the Gospel.


  When they are chosen who are to receive baptism, let their lives be
  examined, whether they have lived honorably while catechumens, whether
  they honored the widows, whether they visited the sick, and whether
  they have done every good work. If those who bring them forward bear
  witness for them that they have done so, then let them hear the
  Gospel.


Paul seems to have presented the Gospel to Corinth as of primary importance.

Hippolytus relates catechumens in 3rd Century Rome being required to "live right' and then, if it was proved that they have for three years, they could then hear the Gospel.  

My question is: Why would the methodology of presenting the Gospel have changed  from Paul's 'presenting it as of primary importance' (see also Phillip and the Eunuch) to that of 'prove you are worthy for 3 years' and then you can hear it?

(A related question is: How could a 3 year instruction in the word be such that the Gospel is not yet heard?  I understand this is probably unanswerable but I can't avoid it.  Say the word and I will edit this out.)
What is Hippolytus’ difference between hearing the Word and hearing the Gospel?

To understand this nuance, we have to take a little trip down memory lane and try to understand what Holy Sacrifice of the Mass and the life of the Catechumens meant in the Early Church?

The Mass in the Early Church as well as the modern Mass of the Ordinary Form are made of various parts.

The first part of the Mass was historically called the Mass of the Catechumensand is now simply called the Liturgy of the Word.


  The Mass (or Liturgy) of the Catechumens is an ancient title for the first half of the Catholic Mass or Eastern Orthodox Divine Liturgy. In the Mass of Paul VI of the Catholic Church, it is referred to as the Liturgy of the Word. It was originally called the Mass of the Catechumens, because the Catechumens, or candidates for Baptism, were required to leave the ceremony before the beginning of the Liturgy of the Eucharist, or Mass, proper.
  
  This exclusion was enforced on the grounds that until Baptism, persons were not fully members of the Church and should not participate in the communal sacrifice that symbolizes and embodies the spiritual union of the Faithful, according to Catholic belief.
  
  In the earliest liturgy there was a service consisting of readings, a homily (explanation of the readings and how to apply them to one's life) and petitionary prayers based on the readings and homily (bidding prayers or prayers of the faithful). 


From the Wikipedia article we can understand that the Liturgy of the Word was in reality both the entire Sacred Texts as well as the Gospels. Since both were employed at Mass it would simply be referred to as the Word, in Hippolytus’ day.

Hearing the Word should be always understood as hearing the Gospel also. Although, the following article is unsure what Hippolytus meant by ”to hear the Gospel”? It would make sense that he was referring to certain mysteries of the faith that were taught by Christ in the Gospels and were thus explained towards the end of their probation as Catechumens, most notably the Eucharist.


  The Ancient Catechumenate
  
  The catechumenate was the ancient church’s process for Christian initiation, leading up to baptism and climaxing with first Eucharist. The earliest post-apostolic picture of the catechumenate comes from The Apostolic Tradition, written by Hippolytus of Rome (d. 235 AD). When newcomers came to the church, Hippolytus insisted that they be interviewed, along with those who brought them, later called sponsors. Sponsors would be questioned whether their guests were “capable of hearing the word” (Cuming 15). These questions were less about motive, and more about lifestyle: Did these inquirers have mistresses? If slaves, did they serve their masters faithfully? Were they gladiators, charioteers, idol-sculptors, actors, brothel-keepers, theatre producers, city magistrates or employed in some other immoral trade (Harmless 41)? If so, they would be required to make the costly choice to “cease or be rejected” (Cuming 15-16). 
  
  Once admitted, catechumens would “hear the word” for three years of instruction, about which little is known. After this period, catechumens and their sponsors would be re-examined, again with attention primarily to lifestyle: “Have they honored the widows? Have they visited the sick? Have they done every good work?” (Cuming 17). If successful, they would be permitted to “hear the gospel,” again a phrase that raises uncertainties about its meaning. Presumably on the weekend leading up to Easter, catechumens would bath, fast and hold vigil in preparation for Baptism and the Eucharist. Following this ritual climax, Hippolytus prescribed further private instruction for the neophytes. 
  
  The fourth century saw the golden age of the catechumenate as a flood of new converts streamed in as a result of Constantine’s endorsement of Christianity. Not surprisingly, this had a marked affect on the nature of the catechumenate. Whereas the few catechumens of the third century could be closely watched regarding attendance and their lifestyles carefully scrutinized, this was no longer feasible in the fourth century (Harmless 58). Moreover, examinations shifted to questions of motivation due to opportunists seeking political advantages (Harmless 58). Importantly, the doctrinal debates within the church and apologetic rhetoric directed at Gnosticism and Arianism resulted in shift to increased catechesis in doctrinal issues. Finally, three stages of the catechumenal process were distinguished: The catechumenate period, Lent and Mystagogy. By 400 AD, an additional stage, Evangelization was added to the beginning of this process indicating that some instruction was appropriate prior to enrollment. 
  
  Ambrose of Milan, the fourth century bishop and catechist who oversaw Augustine’s initiation, described the purpose of the Lenten period as moral education. Ambrose believed that “in order to learn this way of life the competentes needed two things: (1) appropriate models to imitate, and (2) basic moral principles” (Harmless 95). For Ambrose, both of these needs were satisfied with Scripture: the Patriarchs were his chosen models, and the Proverbs were his source of principles. Later, as a catechist himself, Augustine conceived of Lent as a period of “boot camp or Olympic training” “to purge the poisons out of one’s system, to root out slovenly habits, and to sober up with other who sought recovery from an addiction to the world” (Harmless 380).
  
  Mystagogy was the period that followed baptism. While Cyril emphasized the liturgical significance of this period—the Eucharist was now open to the neophyte—Chrysostom stressed the moral nature of this stage. The “gleaming” baptismal robes were to image their “godly conduct and strict discipline” (Chrysostom, Baptismal Instruction, 4.18 and 6.24). In a lament that resonates with the contemporary scene, Chrysostom wrote: “I see many after their baptism living more carelessly than the uninitiated, having nothing particular to distinguish them in their way of life” (Chrysostom, In s. Matthaie evanglium, 4.14). One suspects this sad and familiar state was the outcome of the fourth century prioritization of orthodoxy over orthopraxis. 
  
  As this select review of features of the ancient catechumenate suggests, early Christian initiation gave significant, if not primary, attention to moral and behavioral formation. Thus, its success should be judged by its ability to produce people marked by a Christian way of life.


The Catholic Encyclopedia offers a few insights into this subject matter as follows:


  The catechumens were divided into mere inquirers (audientes, akromeni) and catechumens properly so-called; and in each stage there was a three-fold preparation — **catechetical, ascetical, and liturgical **.
  
  (1) If a pagan wished to become a Christian he was given some elementary instruction in the fundamental doctrines and practices of the Church. He had to show by his conduct that he was in earnest about the step he was about to take. So far, he was only in the stage of inquiry, and was not counted as a Christian at all. He was allowed to be present at the first part of the Mass, but he was dismissed immediately after the sermon.
  
  (2) As soon as his instructors were satisfied that he was likely to persevere, the inquirer was promoted to the rank of catechumen. He was now entitled to be called a Christian, though he was not looked upon as one of the "faithful". "Ask a man, 'Are you a Christian?' He answers, 'No', if he is a pagan or a Jew. But if he says 'Yes', ask him again, 'Are you a catechumen or one of the faithful?'" (St. Augustine, Tractate 44 on the Gospel of John, no. 2).
  
  In the early ages the rites of admission to the catechumenate were quite simple, but in the course of time they became more elaborate. At first the candidates were merely signed on the forehead with the sign of the cross, or hands were imposed on them with suitable prayers; and sometimes both ceremonies were used. Thus St. Augustine in his model of an instruction to an inquirer says: "He should be asked whether he believes what he has heard, and is ready to observe it. If he answers in the affirmative he should be solemnly signed and treated according to the custom of the Church" (solemniter signandus est et ecclesiae more tractandus.-- De Cat. Rud., xxvi, P.L., XL, 344). Eusebius mentions the imposition of hands and prayer (Vita Constantini, iv. 61, P.G., XX, 1213). Among the Latins, and especially at Rome, breathing accompanied with a form of exorcism and placing in the mouth a little exorcised salt, was employed in addition to the signing with the cross and the imposition of hands. Other rites were the opening of the ears (Mark 7:34) and anointing. See Martène, "De Antiquis Ecclesiae Ritibus" (Rouen, 1700), I, where several ordines ad fasciendum Christianum, or catechumenum, are given; Chardon, "Hist. des Sacrements", in Migne's "Theol. Cursus Completus", Paris, 1874, XX, 31 sqq., 149 sqq.
  
  Catechumens when present at Mass were not dismissed with the inquirers, but were detained while a special prayer was recited over them. They then also withdrew before the Mass of the Faithful began. The instruction which they received is described in the article Christian Doctrine. As to their standard of living they had to abstain from all immoral and pagan practices, and give proof by their virtue and works of penance that they were worthy to begin a more immediate preparation for baptism. The duration of this stage was not fixed. In general it lasted long enough to test the dispositions of the catechumen. The council of Elvira alludes to the custom of making it last two years and the civil law fixed it at this (Justinian, Novel. cxliv). But the causes which ultimately led to the abolition of the catechumenate (see above) tended also to shorten it. Thus the Council of Agde (506) allowed even Jews (with regard to whom special caution was required) to receive baptism after eight months preparation; and later on St. Gregory reduced the term to forty days. On the other hand the duration of the catechumenate might be extended, and the catechumen might be reduced to the rank of the audientes, if he was guilty of grave crimes (fifth canon of Neocæsarea, fourteenth canon of Nicaea). What seems extraordinary to our modern notions is that the catechumens themselves put off their baptisms for many years, sometimes even till their last illness. Constantine the Great is an example of this extreme delay. St. Ambrose, St. Basil, St. Gregory Nazianzen, and St. John Chrysostom were not baptized till after their thirtieth year. A question much discussed was the fate of those who died in this stage. As we have seen, they were looked upon as Christians, but not as belonging to the "faithful", because the cleansing waters of baptism had not been poured over their souls. St. Gregory describes his terror during a storm at sea lest he might be taken away unbaptized (Carmen de Vita Sua, 324, sqq., P.G. XXXVII, 994). However, St. Ambrose has no doubt about the salvation of Valentinian the Younger, who has asked for baptism, but had died before the saint could reach him ("De Obitu Valentini.", n. 51, P.L. XVI, 1374). Hence the common teaching was that the defect of baptism might be supplied by desire. This was especially held with regard to those who were in the later stage of immediate preparation, to be described presently. On this whole question see Franzelin, "De Ecclesia" (Rome, 1887), 414 sqq.
  
  (3) When the catechumens had completed this stage of preparation and trial, their names were inscribed among the competentes; i.e. those seeking to be baptized. The Greeks called them photizomenoi. This might mean that they were being enlightened in the mysteries of the faith; or, more probably, that they were being baptized, for the Greeks commonly spoke of baptism as "light" (cf. Hebrews 6:4; 10:32). In this advanced stage they were sometimes called fideles by anticipation (e.g. St. Cyril of Jerusalem, Cat., I, 4; V, 1; P.G., XXXIII, 373, 505). Lent was the time when the three-fold preparation — instructive, ascetical, and liturgical — was carried on. The ascetical preparation was severe. Prayer and fasting naturally formed part of it; but the competentes were also exhorted to keep silence as far as possible and, if they were married, to observe continence. (St. Justin, "Apol.", lxi, P.G., VI, 420; St. Cyril of Jerusalem, Cat., I, sub fin., P.G., XXXIII, col. 376; St. August., "De Fide et Op.", ix, P.L. XL, 205). Confession was also enjoined (Tertullian, "De Bapt.", xx, P.L. I, 1222 where he quotes Matthew 3:6: "they were baptized, confessing their sins". See also St. Cyril, ib.; Eusebius, Life of Constantine IV.61). The instruction given at this time is described in the article [Christian Doctrine, where an account of St. Cyril's "catecheses" will be found.


Catechumens were allowed to be present at the first part of the Mass, but he was dismissed immediately after the sermon. And "Catechumen," in the early Church, was the name applied to one who had not yet been initiated into the sacred mysteries, meaning the mysteries of the Sacred Sacrifice of the Mass, but was undergoing a course of preparation for that purpose. The word occurs in Galatians 6:6: "Let him that is instructed in the word, [ho katechoumenos, is qui catechizatur] communicate to him that instructeth him [to katechounti, ei qui catechizat] in all good things." Other parts of the verb katicksein occur in 1 Corinthians 14:19; Luke 1:4; Acts 18:24. Thus it is not inconceivable that the phrase of hearing the Gospel may have been simply a way of meaning the Sacrifice of the Mass. Thus after their baptism the neophytes were in fullness and understanding of what the words of Jesus Christ meant in regards to the Sacred Mysteries of the faith.


  In the Early Church, catechumens were dismissed after the liturgy of the word because the sacraments, the Sacred “Mysteries,” were a carefully guarded secret open only to the initiated. - The Catechumenate and the Law: A Pastoral and Canonical Commentary


Thus it is more than obvious that St. Hippolytus of Rome was writing in a veiled manner in order to preserve the truths of our holy religion by explaining things in the Early Church thus and guarding the Sacred Mysteries as such. Only after baptism, would the neophytes understand the Gospels properly and without nuances.