One of the challenged points of Calvinism is that of Sovereign (unconditional) election. This states that God has chosen some to be saved and passed over others. People challenge this as unfair, unjust, or just plain unbiblical. So do we see any examples of Sovereign Election in Scripture? Of course we do.
In the Exodus story we see the tenth plague, the plague of death. Exodus 11 says the Lord hardened Pharaoh’s heart against Israel and he did not let them go. Then, in chapter 12, he gives Moses, and by extension Israel, the instructions on how to be passed over by death. These instructions were not given to the Egyptians. They were not chosen to be saved.
The result of this was that the firstborn children of Egypt died that night. Paul even addresses this in Romans 9. Was God unfair? Was God unjust?
What shall we say then? Is there injustice on God’s part? By no means! 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 depends not on human will or exertion, but on God, who has mercy. For the Scripture says to Pharaoh, “For this very purpose I have raised you up, that I might show my power in you, and that my name might be proclaimed in all the earth.” So then he has mercy on whomever he wills, and he hardens whomever he wills.Romans 9:14-18 ESV
God will have mercy on whom he will have mercy. God chose not to have mercy on Egypt. The same way, God chooses not to have mercy on some people today but others he calls by his Sovereign choice to come to a saving faith in Him.