The covenantal promise given to Abraham that through his seed "all the families of the earth shall be blessed" (Genesis 12:3; cf. 18:18, 22:18, 26:4, 28:14). The phrase recurs five times in Genesis — always in the mouth of God, always tied to the patriarchal line. The Hebrew verb (Niphal nibreku) can be read passively ("shall be blessed") or reflexively ("shall bless themselves by"); the NT settles the question by citing it in the passive voice and applying it to the evangelization of the Gentiles (Galatians 3:8, Acts 3:25).
God's covenant with Abraham was never parochial. The call of Israel was always for the sake of the nations — chosen to be a priesthood, not a private club. Israel repeatedly forgot this, and much of her prophetic literature is a summons back to global vision (Isaiah 49:6 — "I will make you as a light for the nations, that my salvation may reach to the end of the earth"; Jonah is a parable against ethnocentric faith). The Great Commission (Matthew 28:19 — "make disciples of all nations") is Abrahamic obedience. Paul understood his whole missionary career as the cashing in of Genesis 12:3: "The Scripture, foreseeing that God would justify the Gentiles by faith, preached the gospel beforehand to Abraham, saying, 'In you shall all the nations be blessed'" (Galatians 3:8). When a Chinese believer or a Somali convert or a Brazilian Pentecostal trusts Christ, a promise made to an elderly Mesopotamian pastoralist four thousand years ago comes true. The Church is Abraham's family photo.