Brothers and sisters, I give an example from daily life: once a person's will has been ratified, no one adds to it or annuls it.
References for Galatians 3:15
Now the promises were made to Abraham and to his offspring; it does not say, "And to offsprings," as of many; but it says, "And to your offspring," that is, to one person, who is Christ.
References for Galatians 3:16
My point is this: the law, which came four hundred thirty years later, does not annul a covenant previously ratified by God, so as to nullify the promise.
For if the inheritance comes from the law, it no longer comes from the promise; but God granted it to Abraham through the promise.