Charles Ellicott Commentary Romans 4:16

"For this cause [it is] of faith, that [it may be] according to grace; to the end that the promise may be sure to all the seed; not to that only which is of the law, but to that also which is of the faith of Abraham, who is the father of us all" — Romans 4:16 (ASV)

Therefore it is of faith.—The words "it is" must be supplied. "It" stands for the Messianic inheritance, or, in common phrase, salvation. Faith on man’s part is correlative with grace on God’s part, and salvation, being thus dependent upon grace, is as wide and universal as grace itself. It knows no restriction of law.

Not to that only which is of the law.—Not only to that part of the human race which belongs to the dispensation of the Law, but also to that part which is, in a spiritual sense, descended from Abraham by imitating his faith.

On verses 14-17

This Messianic kingdom cannot have anything to do with law, for if it did, faith and the promise would cease to have any role. Faith and law cannot coexist; they are the opposites of each other. The proper effect of law is punishment, for law only exposes sin. Faith, on the other hand, is the real key to the inheritance. It sets grace in motion, and grace, unlike law, excludes no one. It is open alike to the legal and the spiritual descendants of Abraham—in other words (as Scripture itself testifies), to all mankind, whom Abraham represents before God.