Is God unjust?
"Just as it is written: 'Jacob I loved, but Esau I hated.' What then shall we say? Is God unjust? Not at all! For He says to Moses, 'I will have mercy on whom I have mercy, and I will have compassion on whom I have compassion.' It does not, therefore, depend on man's desire or effort, but on God's mercy." Romans 9:13-16
Though God is absolutely sovereign, having mercy on whom He will have mercy and hardening whom He will — He is strictly just, both in bestowing His saving mercy upon His elect, and in the everlasting damnation of the reprobate.
"Therefore God has mercy on whom He wants to have mercy, and He hardens whom He wants to harden." Romans 9:18