Now to Abraham and his seed were the promises made. He saith not, And to seeds, as of many; but as of one, And to thy seed, which is Christ. Now to Abraham and his seed - The promise of salvation by faith was made to Abraham and his posterity.
He saith not, And to seeds - It was one particular kind of posterity which was intended: but as of one - which is Christ; i.e. to the spiritual head, and all believers in him, who are children of Abraham, because they are believers, Galatians 3:7. But why does the apostle say, not of seeds, as of many? To this it is answered, that Abraham possessed in his family two seeds, one natural, viz. the members of his own household; and the other spiritual, those who were like himself because of their faith. The promises were not of a temporal nature; had they been so, they would have belonged to his natural seed; but they did not, therefore they must have belonged to the spiritual posterity. And as we know that promises of justification, etc., could not properly be made to Christ in himself, hence we must conclude his members to be here intended, and the word Christ is put here for Christians. It is from Christ that the grace flows which constitutes Christians. Christians are those who believe after the example of Abraham; they therefore are the spiritual seed. Christ, working in and by these, makes them the light and salt of the world; and through them, under and by Christ, are all the nations of the earth blessed. This appears to be the most consistent interpretation, though every thing must be understood of Christ in the first instance, and then of Christians only through him.