In v. 35, Paul poses the picture of a giver who gives to God. He asks the third rhetorical question in v. 34—“Or who has given a gift to him that he might be repaid?” Paul is asking in other words, “From whom has God received a gift that He is now obligated to repay it?” The obvious answer is, no one. God has not received anything from anyone. He is therefore under no obligation to anyone. Why should God repay you anything when God owes you nothing!
This is what Paul has been teaching in Romans. God did not choose to save Israel because they were good. No one is justified by one’s good works but by faith in Christ. No one is sanctified by one’s willpower to live a holy life, but by the power of the Spirit of God. No one is chosen by God by one’s decision to believe in Christ, but by God’s sovereign will. God has saved us by His own decision, through His own power, and for His own glory. God is therefore obligated to no one except Himself.
God then is infinitely independent of any wisdom from others or any obligation to anyone. Instead, everything is dependent for its existence to God.