Progressive revelation — Moses' five books vs later necessity (Hebrews 1:1)
It does not count against this that Scripture as we now have it holds not a few things needful for salvation that are missing from Moses' five books — which alone made up sacred Scripture for a time.
The same things were not necessary for salvation in every age. Much that now belongs of necessity to faith and religion under the New Testament did not always have that necessity.
God did not unveil all the mysteries of heavenly wisdom at once. As the Apostle says in Hebrews, he spoke πολυμερῶς καὶ πολυτρόπως — in many parts and in many ways (Hebrews 1:1). From the first consigning of heavenly teaching to writing, the light of divine revelation grew little by little, until in the last times Christ brought the fullness of that teaching and announced to us the whole counsel of our salvation.
Latin
XXVI. Neque contra hoc facit quod Scriptura, qualis jam est, non pauca ad salutem necessaria continet, quae desiderantur in quinque libris Mosis, quibus solis constitit aliquandiu Scripturae sacrae corpus. Etenim sciendum est omnibus aetatibus non eadem fuisse ad salutem necessaria. Nam plurima nunc sub novo Testamento ad fidem & religionem necessario pertinent, quae non semper eandem habuerunt necessitatem. Siquidem Deus omnia caelestis sapientiae mysteria non revelavit simul & semel: sed ut loquitur Apostolus Hebr. 1. πολυμερῶς καὶ πολυτρόπως multis partibus atque multis modis. Atque, ex quo primum doctrina caelestis scripto consignari coepit, paulatim crevit divinae revelationis lumen, donec ultimis temporibus Christus doctrinae caelestis plenitudinem attulit, & totum de nostra salute consilium nobis annunciavit.