Matthew Poole and continuators on Galatians 3:17

17 And this I say, that the covenant that was before confirmed of God▪ in Christ , the law which was four hundred and thirty years after, cannot disanul , that it should make the promise of no effect .

The word translated Covenant, is the same as before; ordinarily signifying ones disposal of things in his last Will and Testament. Which name is given to the Covenant of Grace, with respect to the Death of Christ; for though Christ as yet had not dyed, yet he was, by vertue of the Covenant of Redemption, and in Gods counsels, The Lamb slain from the foundation of the World, Rev. 13.8. This (he saith) was in Christ, (as Abrahams promised seed,) confirmed of God to Abraham, by Gods Oath, Heb. 6▪ 17, 18. by frequent repetitions of it, by such solemn Rites as covenants use to be confirmed by, Gen. 15.17, 18. By the Seals of Circumcision, Gen. 17.11: Rom. 4.11. By a long prescription, &c. though it received indeed its final and ultimate consummation by the Death of Christ, yet it was before many wayes confirmed.

The Law was given 430 years after the giving this promise to Abraham, though Gen. 15.13. the round number of 400 years only be mentioned: which are to be counted from the birth of Isaac; yet Exod. 12.40. they are reckoned (as here) 430 years, from Abrahams going out of Canaan, Gen. 12.4. from whence to the birth of Isaac were 25 years; Gen. 21.5. compared with chap. 12.4. From the birth of Isaac till Iacob was born, 60 years, Gen. 25.26. From thence till Iacob went down into Egypt, 130; Gen. 47.9. where they abode 215 years.

Hence the Apostle concludes, that it was impossible that the Law, which was not given till 430 years after the confirmation of the promise, should make the promise confirmed of no effect.

Marginal references: Exod. 12.40, 41.; Rom. 4.13, 14.