Romans 9:16, 18-19

Again, this proves that God’s choice doesn’t depend on how badly someone wants it or tries to earn it, but it depends on God’s kindness and mercy.

So again we see that it is entirely up to God to show mercy or to harden the hearts of whomever he chooses. Well then, one might ask, “If God is in complete control, how could he blame us? For who can resist whatever he wants done?”