There are many verses in Scripture that talk of God calling us into fellowship with him. Probably one of the most widely quoted group of verses is in Romans 8 where our calling is a part of God's whole act of foreknowing, predestining, and justifying. Rom 8:29-30 For those whom he foreknew he also predestined to be conformed to the image of his Son, in order that he might be the firstborn among many brothers. 30 And those whom he predestined he also called, and those whom he called he also justified, and those whom he justified he also glorified. In Paul's glorious sentence, no matter what word you look at, you cannot isolate it from the others. If you claim to be justified, it means you have been foreknown, predestined, called, and glorified. This is known as Paul's unbreakable chain, and it is God's glorious power and sovereignty in his electing and saving grace.
We talk of irresistible grace, because of God's power in his sovereign will. If God brings all he foreknows to salvation, it means that God is irresistible in his work of grace. This is a characteristic of God's power that we see all through Scripture. When God speaks to his people about their identity, he reminds us that we are his work. Ephesians 2:8-10 For by grace you have been saved through faith. And this is not your own doing; it is the gift of God, 9 not a result of works, so that no one may boast. 10 For we are his workmanship, created in Christ Jesus for good works, which God prepared beforehand, that we should walk in them.
This is not just applicable to the New Testament church but to all who have been called to be God's people in history. Take for instance how God speaks to the congregation of Israel. Deuteronomy 7:6-8 "For you are a people holy to the LORD your God. The LORD your God has chosen you to be a people for his treasured possession, out of all the peoples who are on the face of the earth. 7 It was not because you were more in number than any other people that the LORD set his love on you and chose you, for you were the fewest of all peoples, 8 but it is because the LORD loves you and is keeping the oath that he swore to your fathers, that the LORD has brought you out with a mighty hand and redeemed you from the house of slavery, from the hand of Pharaoh king of Egypt.
God made Israel his possession and people because he promised beforehand to bring them out of slavery. He had already foreordained that they would go into slavery as part of his plan to do it. Genesis 15:13 Then the LORD said to Abram, "Know for certain that your offspring will be sojourners in a land that is not theirs and will be servants there, and they will be afflicted for four hundred years. God also reminded his people that even their Father Abraham was called out of pagan idolatry by his grace. Joshua 24:2-5 And Joshua said to all the people, "Thus says the LORD, the God of Israel, 'Long ago, your fathers lived beyond the Euphrates, Terah, the father of Abraham and of Nahor; and they served other gods. 3 Then I took your father Abraham from beyond the River and led him through all the land of Canaan, and made his offspring many. I gave him Isaac. 4 And to Isaac I gave Jacob and Esau. And I gave Esau the hill country of Seir to possess, but Jacob and his children went down to Egypt. 5 And I sent Moses and Aaron, and I plagued Egypt with what I did in the midst of it, and afterward I brought you out.
Bottom line, anybody claiming to be a part of the people of God can only do so because of the irresistible sovereign grace of God. That same power of sovereignty that calls us and saves us, is the power that holds us and keeps us. For some, God's irresistible grace might be a theological argument, but for those who contemplate the reality of God's grace it is a reassuring truth that comforts us every day. God loves his church. God has called his church. God is never letting go of his church. Our power to refuse God is impotent against his saving hand. Because of the sovereign power of God's grace, those in Christ can take every one of his promises to the bank.