Galatians 3:15-18 RSVA

15 To give a human example, brethren: no one annuls even a man's will, or adds to it, once it has been ratified.
16 Now the promises were made to Abraham and to his offspring. It does not say, "And to offsprings," referring to many; but, referring to one, "And to your offspring," which is Christ.
17 This is what I mean: the law, which came four hundred and thirty years afterward, does not annul a covenant previously ratified by God, so as to make the promise void.
18 For if the inheritance is by the law, it is no longer by promise; but God gave it to Abraham by a promise.