When God chooses a man to be saved, He chooses according to His foreknowledge. But, what is God's foreknowledge? That is a debated subject. Let's first look at Scripture.
Romans 8:28-30
(28) And we know that God causes all things to work together for good to those who love God, to those who are called according to His purpose. (29) For those whom He foreknew, He also predestined to become conformed to the image of His Son, so that He would be the firstborn among many brethren; 30and these whom He predestined, He also called; and these whom He called, He also justified; and these whom He justified, He also glorified.
Everyone that is saved or will be saved (using the terms of Romans 8.29-30: everyone who is or will be “justified” and “glorified”) has been foreknown by God. This is clear from the passage. No one disputes this truth. But again, what does it mean when the text says, "He foreknew?"
Foreknowledge is not mere "foresight"
People that say man is ultimately responsible for his own salvation (that man is completely free to choose to be saved) interpret “foreknowledge” to mean “foresight” (looking off into the future). They say that before creation, God looked into the future to see who would believe. When He discovered who would believe, he "determined" that these would be saved. So, according to this understanding God’s choice of who will be saved is based upon each man's choice to be saved by God. Actually, it would be man's theoretical choice to be saved.
Is this what the Apostle Paul meant by “foreknowledge?” This sounds like a pretty good understanding at first. Foreknowledge certainly sounds like knowing something before it happens. Unfortunately, this is not what the word, "foreknowledge" means. We must make an attempt to understand the word from the context of Scripture.
Discovering the meaning throughout Scripture
The Greek word for foreknowledge is “prognosis.” It comes from the Greek word, “ginowsko,” meaning ‘to know.’ We know from the usage of the word, “ginowsko,” that this “knowledge” means more than knowledge of facts when God is the One that is doing the “knowing.” To see the meaning of the word we need to look at the way it is used in the New Testament and in the Greek translation of the Old Testament (LXX, Septuagint; this is the translation that Jesus and many of the NT writers quoted from).
Jeremiah. Let's consider God's 'knowledge' of Jeremiah.
Jeremiah 1:5
“Before I formed you in the womb I knew you, And before you were born I consecrated you; I have appointed you a prophet to the nations.”
God knew Jeremiah. The 'knowing' referred to in the verse is the same as the 'consecrating' (the terms are grammatically parallel). This knowing and consecrating happened before Jeremiah was born. God was choosing ('consecrating') Jeremiah at the same time He was 'knowing' him. Note also that God was 'knowing' Jeremiah – not mrely facts about Jeremiah. It wasn’t an intellectual knowledge, but a personal knowledge.
Adam and Eve. Let's consider Adam's 'knowledge' of Eve.
Genesis 4:1
Now the man had relations with his wife Eve, and she conceived and gave birth to Cain, and she said, “I have gotten a manchild with the help of the Lord.”
Adam knew Eve (“knew” = “had relations”). This is referring to a personal knowledge. It resulted in the conception of a child.
Moses. Let's consider God's 'knowledge' of Moses.
Exodus 33:17
The Lord said to Moses, “I will also do this thing of which you have spoken; for you have found favor in My sight and I have known you by name.”
Exodus 33:22
and it will come about, while My glory is passing by, that I will put you in the cleft of the rock and cover you with My hand until I have passed by.
God knew Moses by name. God is saying much more than that He knew what Moses’ name would be. He knew Moses personally. This was a personal knowledge. God was indicating to Moses that He had made a decision to have a personal relationship with Moses.
Israel. Let's consider God's 'knowledge' of the Nation of Israel.
Amos 3:2
“You only have I chosen among all the families of the earth; Therefore I will punish you for all your iniquities.”
God says that He knew Israel. The word, “chosen” is the same word that we have been looking at. It is the Greek word often translated “know.” Obviously, this is more than an intellectual knowledge since God “knew” about the existence of other people. God chose to know the Nation of Israel in a special way.
Christ's sheep. Let's consider Christ's 'knowledge' of His sheep.
John 10:14-15
“I am the good shepherd, and I know My own and My own know Me, (15) even as the Father knows Me and I know the Father; and I lay down My life for the sheep.
Jesus Christ knows His sheep. Again, this is a personal knowledge.
Believers. Let's consider Christ's 'knowledge' of true believers.
Matthew 7:23
“And then I will declare to them, ‘I never knew you; depart from Me, you who practice lawlessness.’
It is evident that God does not “know” certain ones. He does not have a personal relationship with everyone. God is all-knowing (omniscient). He certainly knows everything about every person, but He does not know everyone personally. He does not choose to have a relationship with everyone personally.
2 Timothy 2:19
Nevertheless, the firm foundation of God stands, having this seal, “The Lord knows those who are His,” and, “Everyone who names the name of the Lord is to abstain from wickedness.”
“The Lord knows those who are His.”
Romans 8:29
29For those whom He foreknew, He also predestined to become conformed to the image of His Son, so that He would be the firstborn among many brethren;
Here God knows people – not merely actions of people, nor facts about people. Also, God is active (as He was in knowing Moses, Israel, and Jeremiah). He was choosing. He is not passively “noticing” something. He actively knows people.
A couple conclusions
We have seen that God’s knowledge (ginowsko) and foreknowledge is:
1. Active – it is something He initiates; He is not passive in the matter. He is not simply noticing something or discovering something.
2. Personal – He is knowing and foreknowing people. It is not a knowledge of mere facts.
So, God's foreknowledge (which is the basis for his choosing of men to be saved) does not refer to his discovery of facts about people. God's foreknowledge is God's active choice to know people personally.
More confirmation from Scripture
This understanding is confirmed in Romans 11.2.
Romans 11:2
God has not rejected His people whom He foreknew. Or do you not know what the Scripture says in the passage about Elijah, how he pleads with God against Israel?
According to this passage God 'foreknew' Israel. Deuteronomy 7.6-7 tells us the same thing, but notice the qualification that goes along with it.
Deuteronomy 7:6-7
6“For you are a holy people to the Lord your God; the Lord your God has chosen you to be a people for His own possession out of all the peoples who are on the face of the earth. 7“The Lord did not set His love on you nor choose you because you were more in number than any of the peoples, for you were the fewest of all peoples,
God did not foreknow that Israel would be faithful and mighty. He foreknew them (He chose to have a special relationship with them) in spite of who they were. That is the point of Deuteronomy 7:6-7. Romans 11:2 says God has not rejected Israel whom He chose to have a special relationship with and give a special blessing to.
One more thing
Acts 2:23 appears to contradict our understanding of foreknowledge.
Acts 2:23
this Man [Christ], delivered over by the predetermined plan and foreknowledge of God, you nailed to a cross by the hands of godless men and put Him to death.
In this verse the object foreknown might appear at first glance to be an action, but it is in fact Christ. It might appear at first glace to say God foreknew what would happen (certain facts) and then determined it would be so. But, how could this be? Surely we wouldn’t say that God looked ahead and saw what His Son was going to do, and then determined that it would be so. That is ridiculous!
The verse is saying God chose Christ to be the Redeemer and determined that He would die in the place of sinners. God determined to have a special relationship with Christ. God the Father gave His Son a gift (all believers), a bride. He singled out Christ as the One Who would redeem men. He didn't simply discover that Christ was going to redeem men, and then agree or affirm that it is so. God the Father determined it. He chose Christ to be the Redeemer of all mankind (not every man, but every man would would believe).
Conclusion
So, according to Romans 8:28-29, God determined to know some. All those that He determined to know, He predestined to be saved. Those predestined were called. This is the “irresistible call” since every single one that is called accepts the call and is justified and glorified.
Have you been justified? Did you hear and accept God's call? If yes, then God foreknew you a long time ago. He determined to know you before you were born! Your salvation - justification and glorification - was set in stone before you existed! You are saved, not because of your innate goodness, but because God chose to show you grace and mercy. Give thanks to the Lord!