Genesis 12.3, especially the last line, is the centerpiece of the Bible, the foundation upon which the rest of the biblical message is built, for everything that follows God’s promise to Abraham,
develops this promise,
“I will bless those who bless you,
And I will curse him who curses you;
And in you all the families of the earth shall be blessed.”
The rest of the Bible shows how God worked to fulfill that grand promise, so that the history of Israel is the history God fulfilling this promise, because He used Israel to bring about the blessing for all the families of the earth!
Then the New Testament shows its fulfillment,
“You are sons of the prophets, and of the covenant which God made with our fathers, saying to Abraham, ‘And in your seed all the families of the earth shall be blessed.’ To you first, God, having raised up His Servant Jesus, sent Him to bless you, in turning away every one of you from your iniquities” (Acts 3.25, 26).
“And the Scripture, foreseeing that God would justify the Gentiles by faith, preached the gospel to Abraham beforehand, saying, ‘In you all the nations shall be blessed'” (Gal 3.8).
Then in the following passages, you can see how it is true that the Lord includes people from every nation,
“There is neither Jew nor Greek, there is neither slave nor free, there is neither male nor female; for you are all one in Christ Jesus. And if you are Christ’s, then you are Abraham’s seed, and heirs according to the promise” (Gal 3.28, 29).
“After these things I looked, and behold, a great multitude which no one could number, of all nations, tribes, peoples, and tongues, standing before the throne and before the Lamb, clothed with white robes, with palm branches in their hands” (Rev 7.9).
“Then one of the elders answered, saying to me, ‘Who are these arrayed in white robes, and where did they come from?’ And I said to him, ‘Sir, you know.’ So he said to me, ‘These are the ones who come out of the great tribulation, and washed their robes and made them white in the blood of the Lamb'” (Rev 7.13, 14).