What shall we say then? There is no injustice with God, is there? May it never be! For He says to Moses, “I WILL HAVE MERCY ON WHOM I HAVE MERCY, AND I WILL HAVE COMPASSION ON WHOM I HAVE COMPASSION.” So then it does not depend on the man who wills or the man who runs, but on God who has mercy.
God is not responsible for humanity’s predicament. Human beings, because of the disobedience in the garden of Eden, are responsible for their condition in sin, disobedience, and coming judgment. Further, it is important to remember that God does exercise mercy with absolute freedom. Therefore, it is not unjust for him to do so, for God is not unjust. In fact, whatever he does is right. God himself is the standard of right and wrong. Election and reprobation are both divine prerogatives.
Since his audience recognized the authority of Scripture, Paul turned to the Word of God for evidence of the truth of his message. He cites the words that God spoke to Moses in Exodus 33:19, “I will have mercy on whom I will have mercy, and I will have compassion on whom I will have compassion (cf. v. 15). Even though Israel had failed abysmally before Yahweh, he nevertheless acted in mercy toward them, and he acts in mercy sovereignly.
Thus, the apostle concludes, “It does not, therefore, depend on man’s desire or effort, but on God’s mercy” (cf. v. 16). If ever a text indicated the unscriptural nature of “free will,” this one does. “It is not of him that wills,” the apostle says in the original Greek. The doctrine of free will—that it is in the power of a man to turn to God by himself—is contrary to the grace of God. Salvation becomes, then, the work of God and the work of man, and the purity of the grace of God is compromised. Salvation is only of the Lord.
Man is unable to come to God of and by himself. Jesus put it as strongly as anyone in Scripture: “No one can come to me unless the Father who sent me draws him, and I will raise him up at the last day” (John 6:44). We are unable to make a decision of the will for God and salvation until God has first worked in our will sot make us willing. Salvation is first of his willing (cf. James 1:18), and only then, of our response of faith.
— S. Lewis Johnson, Discovering Romans: Spiritual Revival for the Soul, (Grand Rapids: Zondervan, 2014), 158.