Is there an explanation in Catholicism as to why it was the Son and not the others of the Blessed Trinity to become man and be crucified for our sake? According to Catholic faith and theology, once God decreed to save mankind, redemption would be by the work of God-made-man.


  For us men and for our salvation,
  he came down from heaven: 
  [...]
  and became man.
  For our sake he was
  crucified. - The Nicene Creed.


And


  But God decided that man should be shown mercy and be pardoned. His
  mercy was to be above all His works; and He also decreed that this
  mercy and pardon were to be granted because of the full satisfaction
  of justice by adequate atonement. Hence it became necessary that One
  of the Trinity assume created nature and in that nature offer
  reparation to God for man's great sin. - Library: The theology of
  the Precious Blood | Catholic Culture.


Within Catholicism is there an explanation of why it was the Son and not the Father or the Holy Spirit who for us men and our salvation became man and was crucified?
St. Thomas Aquinas addresses this question in Summa Theologica III q. 3 a. 8 (&quot;Whether it was more fitting that the Person of the Son rather than any other Divine Person should assume human nature?&quot;) c.:

It was most fitting that the Person of the Son should become incarnate. First, on the part of the union; for such as are similar are fittingly united. Now the Person of the Son, Who is the Word of God, has a certain common agreement with all creatures, because the word of the craftsman, i.e. his concept, is an exemplar likeness of whatever is made by him. Hence the Word of God, Who is His eternal concept, is the exemplar likeness of all creatures. And therefore as creatures are established in their proper species, though movably, by the participation of this likeness, so by the non-participated and personal union of the Word with a creature, it was fitting that the creature should be restored in order to its eternal and unchangeable perfection; for the craftsman by the intelligible form of his art, whereby he fashioned his handiwork, restores it when it has fallen into ruin. Moreover, He has a particular agreement with human nature, since the Word is a concept of the eternal Wisdom, from Whom all man's wisdom is derived. And hence man is perfected in wisdom (which is his proper perfection, as he is rational) by participating the Word of God, as the disciple is instructed by receiving the word of his master. Hence it is said (Ecclus. 1:5): &quot;The Word of God on high is the fountain of wisdom.&quot; And hence for the consummate perfection of man it was fitting that the very Word of God should be personally united to human nature.
Secondly, the reason of this fitness may be taken from the end of the union, which is the fulfilling of predestination, i.e. of such as are preordained to the heavenly inheritance, which is bestowed only on sons, according to Rm. 8:17: &quot;If sons, heirs also.&quot; Hence it was fitting that by Him Who is the natural Son, men should share this likeness of sonship by adoption, as the Apostle says in the same chapter (Rm. 8:29): &quot;For whom He foreknew, He also predestinated to be made conformable to the image of His Son.&quot;
Thirdly, the reason for this fitness may be taken from the sin of our first parent, for which the Incarnation supplied the remedy. For the first man sinned by seeking knowledge, as is plain from the words of the serpent, promising to man the knowledge of good and evil. Hence it was fitting that by the Word of true knowledge man might be led back to God, having wandered from God through an inordinate thirst for knowledge.

The objections to the question and St. Thomas's replies are interesting, too.