Galatians 3:15

I speak after the manner of men--I take an illustration from a merely human transaction of everyday occurrence. but a man's covenant--whose purpose it is far less important to maintain. if it be confirmed--when once it hath been ratified. no man disannulleth--"none setteth aside," not even the author himself, much less any second party. None does so who acts in common equity. Much less would the righteous God do so. The law is here, by personification, regarded as a second person, distinct from, and subsequent to, the promise of God. The promise is everlasting, and more peculiarly belongs to God. The law is regarded as something extraneous, afterwards introduced, exceptional and temporary (Gal 3:17-19, Gal 3:21-24). addeth--None addeth new conditions "making" the covenant "of none effect" (Gal 3:17). So legal Judaism could make no alteration in the fundamental relation between God and man, already established by the promises to Abraham; it could not add as a new condition the observance of the law, in which case the fulfilment of the promise would be attached to a condition impossible for man to perform. The "covenant" here is one of free grace, a promise afterwards carried into effect in the Gospel.

The apostle in this chapter, I. Reproves the Galatians for their folly, in suffering themselves to be drawn away from the faith of the gospel, and endeavours, from several considerations, to impress them with a sense of it. II. He proves the doctrine which he had reproved them for departing from - that of justification by faith without the works of the law, 1. From the example of Abraham's justification. 2. From the nature and tenour of the law. 3. From the express testimony of the Old Testament; and, 4. From the stability of the covenant of God with Abraham. Lest any should hereupon say, "Wherefore then serveth the law?" he answers, (1.) It was added because of transgressions. (2.) It was given to convince the world of the necessity of a Saviour. (3.) It was designed as a schoolmaster, to bring us to Christ. And then he concludes the chapter by acquainting us with the privilege of Christians under the gospel state.

3:15-18 Christ, not the law, has fulfilled the promise and covenant given to Abraham. 3:15 An irrevocable agreement, such as a person’s last will and testament, is unalterable after the person has died, and it must be executed exactly as written.