Again, Paul is not saying anything new, but is quoting from the Torah and Tanach.
Neh 9:29 And testifiedst against them,
that thou mightest bring them again unto thy law: yet they dealt proudly, and
hearkened not unto thy commandments, but sinned against thy judgments,
(which if a man do, he shall live in them
and withdrew the shoulder, and hardened their neck, and would not hear.
Hab 2:4 Behold, his soul which is lifted up is not upright in him:
but the just shall live by his faith.
Rom 1:17 For therein is the righteousness of God revealed from faith to faith: as it is written,
The just shall live by faith.
Rom 1:18 For the wrath of God is revealed from heaven
against all ungodliness and unrighteousness of men, who
hold the truth in unrighteousness;
Rom 1:19 Because
that which may be known of God is manifest in them; for God hath shewed it unto them.
If one understands the OT scriptures, then one will understand what Paul is saying. Paul is not changing the OT, no, that would be mocking Yah who never changes. Paul is not changing the message, he is fully preaching (pleroo) the OT, same as Jesus/Y'shua fully preached (fulfill/pleroo) the Torah and prophets.