Romans 11:34 - Albert Barnes' Notes on the Bible

For who hath known? ... - This verse is a quotation, with a slight change, from Isaiah 40:13, “Who hath directed the Spirit of the Lord, or being his counsellor hath taught him?” It is designed to express the infinite wisdom and knowledge of God, by affirming that no being could teach him, or counsel him. Earthly monarchs have counsellors of state, whom they may consult in times of perplexity or danger. But God has no such council. He sits alone; nor does he call in any or all of his creatures to advise him. All created beings are not qualified to contribute anything to enlighten or to direct him. It is also designed to silence all opposition to his plans, and to hush all murmurings. The apostle had proved that this was the plan of God. However mysterious and inscrutable it might appear to the Jew or the Gentile, yet it was his duty to submit to God, and to confide in his wisdom, though he was not able to trace the reason of his doings.