Pertaining to Genesis 12:3 "I will curse those who curse you" is God referring only to unbelievers in Jesus?

I would set that passage alongside Matthew 25:31-46, the parable of the Sheep and the Goats.

One is a blessing for those who bless the Jews and a curse for those who harm the Jews. The second is a blessing for those who bless Christians and a curse for those who harm Christians.

The blessings and curses could be temporal or eternal. In the absence of saving faith, any blessing is likely temporal and will not result in salvation. However during times of severe persecution against either Jews or Christians, the very act of helping such a person becomes an act of faith and can save.

Conversely, among the elect, hurting a Jew or a Christian will result not in loss of salvation but may lead to a loss of rewards. Among the reprobate, hurting a Jew or Christian could lead to both temporal and eternal punishment.

Appropriating the blessings upon Abraham for Christians can be justified in light of Paul's grafting analogy in Romans 11. If Christians are grafted into the olive tree that is the true Israel, then the promises made to Abraham are inherited by Christians. However, using Romans 11 in an extreme way leads to Replacement Theology, so you have to be careful. Not all promises made to Israel carry over to Christians, because Israel retains a distinct identity as a subject of Bible prophecy. Since Matthew makes a similar promise to Christians in the parable of the sheep and the goats as the blessing upon Abraham, one can safely assume that this is one promise that does carry over.

A word about cursing vs. punishment.

In the Old Testament, cursing is treated something distinct from punishment. Here is what God thinks about cursing.

"And just as the Lord took delight in making you prosperous and numerous, so the Lord will take delight in bringing you to ruin and destruction; you shall be plucked off the land that you are entering to possess." (Deuteronomy 28:63 NRSVCE)

God is just as happy to send curses--curses that will ruin your life forever--as He is to send blessings. Now let us look at His attitude towards punishment:

"for He does not willingly afflict or grieve anyone." (Lamentations 3:33 NRSVCE)

"For I have no pleasure in the death of anyone, says the Lord God. Turn, then, and live." (Ezekiel 18:32 NRSVCE)

God is not happy when He has to punish someone. According to the Bible, it gives Him no joy.

Therefore God sees cursing (though horrific) as good and something He enjoys just as much as blessing, but punishment as bad. One reason might be because cursing is often a way to save an unjust man from being punished.

Several Promises In all the chapters dealing with Abraham, God gave several promises. As Paul noted, some deal with Jesus's future appearing (the Seed). Some deal with the Land his descendants would occupy as a nation. And importantly, one promise dealt with the arrival of a son to carry on his line of descendants.

But scholars must be careful not to lump all these together. Decades, generations, and millennia separate their fulfilments. So here as well. (Genesis 12:3) This promise of blessing and cursing was given to Abraham, personally and specifically.

Abraham had left his familiar homeland and was venturing out into the unknown. But God wanted Abraham to know that he was not going alone. God would be vitally involved in his undertaking and would be superintending over his welfare.

I will bless them that bless thee, and curse them that curse thee. (Genesis 12:3)

Overreaching Readers of this verse, and particular promise, must not become guilty of overreaching. This cannot be interpreted to mean that no matter what, the Nation of Israel, which was much later established, was never to be confronted or judged by other peoples or nations. God clearly stated in Deuteronomy that the nation of Israel was subject to accountability and obedience to God's laws in order to have His blessing. (Deut. 28) God is, in this Genesis promise, telling the person of Abraham that the Canaanite nations around him would be dealt with according to the way they help or hinder the destiny of Abraham! None of them would stand in the way of God's exaltation of Abraham! If they helped Abraham, God would reciprocate with blessings on them. If they attacked him, they would have God to deal with!

It is a far jump to the conclusion that this promise meant the modern state of affairs concerning the modern nation of Israel. Or how other nations treat the Jews. We are living in a NEW TESTAMENT ERA in which God looks at all peoples equally. In this day and age each person is going to be held accountable for his own actions, good or bad towards others.

It is not a valid conclusion that unbelievers, pagans, and the unregenerate, will be "blessed" by God in their lives simply because they are kind to the Israeli nation. God doesn't reward sin. Nor is the curse applicable to only unbelievers who hate Jews...all anti-semites will be judged even though they claim to be Christian...in the sense that everyone who hates his neighbor will be judged! Love your neighbor is one of the great commandments, along with Love God.

It is a safe approach in exegesis to recognize that promises have different time frames and different applications to people. And that God now requires that all men repent in every nation, Jew and Gentile, in order to receive His approval.

Of a truth I perceive that God is no respector of persons. But in every nation, he that feareth Him, and worketh righteousness, is accepted with Him. (Acts 10:34-35)

I would therefore put you in remembrance...how that the LORD, having saved the people out of the land of Egypt, afterward destroyed them that believed not...But ye beloved, building up yourselves in the most holy faith, praying in the Holy Spirit, keep yourselves in the love of God, looking for the mercy of our Lord Jesus Christ unto eternal life. (Jude 1: 5,20-21)