God's Legally Binding Promise

"To speak in terms of human relations, brethren, [if] even a man makes a last will and testament (a merely human covenant), no one sets it aside or makes it void or adds to it when once it has been drawn up and signed (ratified, confirmed). Now the promises (covenants, agreements) were decreed and made to Abraham and his Seed (his Offspring, his Heir). He [God] does not say, And to seeds (descendants, heirs), as if referring to many persons, but, And to your Seed (your Descendant, your Heir), obviously referring to one individual, Who is [none other than] Christ (the Messiah). This is my argument: The Law, which began 430 years after the covenant [concerning the coming Messiah], does not and cannot annul the covenant previously established (ratified) by God, so as to abolish the promise and make it void. For if the inheritance [of the promise depends on observing] the Law [as these false teachers would like you to believe], it no longer [depends] on the promise; however, God gave it to Abraham [as a free gift solely] by virtue of His promise." (Galatians 3:15-18 - Amplified Bible)

To illustrate his point, Paul uses an example, which everyone understands. If two men make a contract, once it is signed, no one can legally change it. It cannot be revoked and it cannot be added to unilaterally.

God made a promise to Abraham. This promise was in the form of a legally binding contract under the customs of his time. God made this contract not with Abraham only but also with his Seed, who is Jesus Christ.

Legally, God could not change this contract. The law given hundreds of years later can not annul the previous agreement. God must keep His promise. He promised to bless the Gentiles in Christ.