In Genesis 12.3, the Lord promised Abraham that in him all the families of the earth would be blessed, but Genesis 22.18 takes that promise and specifies that the blessing would come through
“In your seed all the nations of the earth shall be blessed, because you have obeyed My voice” (Genesis 22.18).
Galatians 3.16 helps us to see that God intentionally used the singular when speaking of Abraham’s seed, and that the Seed was Jesus Christ,
“Now to Abraham and his Seed were the promises made. He does not say, ‘And to seeds,’ as of many, but as of one, ‘And to your Seed,’ who is Christ” (Galatians 3.16).
In verse 14 Paul had written of the blessing of Abraham,
“…that the blessing of Abraham might come upon the Gentiles in Christ Jesus, that we might receive the promise of the Spirit through faith” (Galatians 3.14).
Earlier in verse 8, the apostle had quoted Genesis 12.3,
“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'” (Galatians 3.8).
Therefore, the magnificent promises made to Abraham, starting in Genesis 12.3, shows that from the very beginning God intended them for the whole world, and Israel would experience those blessings first, and then Israel would introduce those wonderful things to the world, which they did through the preaching of the apostles.