“For if the inheritance be of the law, it is no more of promise: but God gave it to Abraham by promise.”
King James Version (KJV)
3:18 And again - This is a new argument. The former was drawn from the time, this from the nature, of the transaction. If the eternal inheritance be obtained by keeping the law, it is no more by virtue of the free promise - These being just opposite to each other. But it is by promise. Therefore it is not by the law.
Ga 3:18 For if the inheritance [be] of the law, [it is] no more of promise. Law and promise exclude each other. The legal heir receives his inheritance by law, if there be no will; one not a legal heir may receive it by the promise of a will. But God gave [it] to Abraham by promise. The inheritance was given to Abraham by promise; and ours depends on the promise.