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John 1; 9The true light that gives light to every man was coming into the world.[2] 10He was in the world, and though the world was made through him, the world did not recognize him. 11He came to that which was his own, but his own did not receive him. 12Yet to all who received him, to those who believed in his name, he gave the right to become children of God-- 13children born not of natural descent,[3] nor of human decision or a husband's will, but born of God.

The children of God are born of God(regenerated from the spiritual death that resulted from Adam's sin.), not of human decision but by God's decision.

Romans 9

14 What shall we say then? Is there unrighteousness with God? Certainly not! 15For He says to Moses, "I will have mercy on whomever I will have mercy, and I will have compassion on whomever I will have compassion."[1] 16So then it is not of him who wills, nor of him who runs, but of God who shows mercy.

It's not of human will or decision, but God's Mercy and God's Will to have mercy on whomever He chooses to have mercy.