In the "Creed of Athanasius" does "before all things" mean "sooner" or "most important"? Please see this question for why I think the Creed claims to be the declaration of the catholic church rather than merely clarifying the catholic position regarding the doctrine of "Trinity":

The creed starts out like this:


  Quicumque vult salvus esse, ante omnia opus est, ut teneat catholicam
  fidem: Quam nisi quisque integram inviolatamque servaverit, absque
  dubio in aeternum peribit. Fides autem catholica haec est: ut unum
  Deum in Trinitate, et Trinitatem in unitate veneremur. Neque
  confundentes personas, neque substantiam separantes....
  
  Whosoever will be saved, before all things it is necessary that he
  hold the catholic faith. Which faith except every one do keep whole
  and undefiled; without doubt he shall perish everlastingly. And the
  catholic faith is this: That we worship one God in Trinity, and
  Trinity in Unity; Neither confounding the Persons; nor dividing the
  Essence... 


Athanasian Creed on Wikipedia

Is the creed saying that the Trinity dogma should be the first thing that one is taught? Or that believing this creed in its entirety is more important than any other matter of faith than anything else?

In particular are we to understand the creed as saying that "This is the body of truth of the catholic church and it is upon the belief and embrace of the contents of this creed that determine whether or not you will be saved."
According to Lewis &amp; Short, on the entry for ante, the phrase ante omnia can mean “before all things,” but I believe the latter is more appropriate to the context of the creed, wherein it means “above all [things],” i.e., above all else; more than anything.

(α).  Before all things, first of all: “alvus ante omnia ducitur,” Cels. 7, 30: “oportet autem ante omnia os nudare,” id. 8, 2: “Ante omnia instituit, ut etc.,” Suet. Ner. 32; id. Calig. 21: “Ante omnia autem, fratres, etc.,” Vulg. Jac. 5, 12; ib. 1 Petr. 4, 8.—
(β).  Comparatively, above all, especially, chiefty: “publica maestitia eo ante omnia insignis, quia matronae annum, ut parentem, eum luxerunt,” Liv. 2, 7; 7, 4: “quae natura multis et ante omnia ursis,” Plin. 8, 35, 53, § 125: “dulces ante omnia Musae,” the Muses pleasing above all things, Verg. G. 2, 475; id. E. 2, 72: “deformem et taetrum ante omnia vultum,” Juv. 10, 191.—

In addition, on the entry for opus, the phrase opus est means “it is necessary.”

Opus est, it is needful, wanting; there is need of, use for: opus est mihi, tibi, etc., I (thou, etc.) have need of, need, want. It is contrasted with necesse est: emas non quod opus est, sed quod necesse est. Quod non opus est, asse carum est, Cato ap. Sen. Ep. 94, 28. Also with indigere: “ait (Chrysippus) sapien. tem nullā re indigere, et tamen multis illi rebus opus esse, contra stulto nullā re opus est, nullā re enim uti scit, sed omnibus eget,” Sen. Ep. 9, 12. The person who needs any thing is put in the dat., and the thing needed in the nom. or abl. (prop. abl. instrum.: opus est mihi, I have work with, i. e. I need), rarely in the gen., acc., inf., acc. and inf., or with ut.

Thus, the phrase ante omnia opus est, ut teneat catholicam fidem would mean “above all else, it is necessary to possess the Catholic belief (faith).”
@WoundedEgo wrote,

The astute will notice that there is no mention of the resurrection.

On the contrary, the astute would notice there is mention of the resurrection of the dead:

Furthermore, it is necessary to everlasting salvation; that he also believe faithfully...rose again the third day from the dead. He ascended into heaven, he sitteth on the right hand of God the Father Almighty, from whence he will come to judge the living and the dead. At whose coming all men will rise again with their bodies...


References
Lewis, Charlton T.; Short, Charles. Harper’s Latin Dictionary: A New Latin Dictionary Founded on the Translation of Freund’s Latin-German Lexicon. New York: American Book, 1879.