God having from the foundation of the world promised to bring forth the ‘Seed of the woman,’ to work out the redemption of his elect in the conquest of Satan, did, in the separation of Abraham from the rest of the world, begin to make provision of a peculiar stock, from whence the Seed of the woman should spring. That this was the cause and end of his call and separation is evident from hence, that immediately thereupon God assures him that ‘in his seed all the kindreds of the earth should be blessed,’ Gen. 12:1–3, 22:18; which is all one as if he had expressly said to him, ‘For this cause have I chosen and called thee, that in thee I might lay a foundation of bringing forth the promised Seed, by whom the curse is to be taken away, and the blessing of everlasting life procured,’ as Gal. 3:13, 14. For this cause was his posterity continued in a state of separation from the rest of the world, that He might seek a godly seed to himself, Num. 23:9; Mal. 2:15: for this cause did he raise them into a civil, regal, and church state, that he might in them typify and prefigure the offices and benefits of the promised Messiah, who was to gather to himself the nations that were to be blessed in the seed of Abraham, Gen. 49:10; Ps. 45; Hos. 3:5; Ezek. 34:23. And all their sacrifices did but shadow out that great expiation of sin which he was to make in his own person.
An Exposition of the Epistle to the Hebrews, Vol. 3 (Edinburgh; Johnstone and Hunter; 1854) p. 12-13.