Gregory the Dialogist

I will repeat my knowledge from the beginning. But because, on the mention of knowledge, his pride of heart hath displayed itself in his voice, he is plainly discovered to be a haughty person, if he does not quickly conceal himself by some disguise. Whence in concealing his own arrogance, he immediately introduces the righteousness of the Lord, and says, And I will prove my Maker just. In order that, while he speaks as if in behalf of God's righteousness, whatever escapes from him arrogantly, may be excused in the judgment of man.

Morals on the Book of Job, Book XXVI ↗

Thomas Aquinas

Since he intends to introduce reasons a second time against both of these ideas, he says, "I will take up my argument from the beginning," for against everything which has been said from the beginning, I will again adduce arguments which support my opinion. He shows this is his duty saying, "and my Maker," God who made me, "I will prove just." I will show there is no evil in his judgment which you, Job want to charge him with so that you may assert that you are just.

Commentary on Job ↗