Galatians 3:15-17 Amplified Bible, Classic Edition (AMPC)
15 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).
16 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).
17 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.