Galatians 3:15-18 meaning

Paul makes the argument that God's promise to Abraham referred to his seed (i.e. one descendant, Jesus). Paul is probably referring to either of the following verses. It should be noted that the Hebrew word translated "descendants" is "zera" the singular form of the word for "Seed" But most Bibles translate "zera" into the plural "descendants".

"I will establish My covenant between Me and you and your descendants(Seed) after you throughout their generations for an everlasting covenant, to be God to you and to your descendants(Seed) after you."
(Genesis 17:7)

"In your Seed all the nations of the earth shall be blessed, because you have obeyed My voice."
(Genesis 22:18)

Paul states that the fulfillment of this promise to Abraham was In the person of Jesus. The law had nothing to do with it.

It is interesting to note that Paul's argument here turns on the Bible's use of a singular rather than plural noun. Paul points out the Bible says seed rather than seeds. Jesus validated this sort of attention to detail in Scripture. He said in Matthew 5:18, "For truly I say to you, until heaven and earth pass away, not the smallest letter or stroke shall pass from the Law until all is accomplished." Every letter of the Bible is put there by God and will come to pass. The fact that "seed" has no "s" to make it plural tells us Jesus is the fulfillment of the promise that all nations will be blessed.

It is this promise that the Gentile believers in the region of Galatia are benefiting from. The primary point is that they are benefitting from Christ and the promise of God, not the law. The law had nothing to do with Abraham or God's promise to Abraham. The Law came four hundred and thirty years after God's promise to Abraham.

Paul also points out that the Law was not an amendment or a change to the promise. More importantly, it did not nullify the promise. Something promised through Abraham could not be changed by a Law established 430 years later. The inheritance is based on a promise, not a set of rules. God granted it to Abraham by means of a promise, and Gentles (such as the Galatians) inherit the promise the same way as Abraham: by believing.