And he received the sign ... - A sign is that by which any thing is shown, or represented. And circumcision thus showed that there was a covenant between Abraham and God; Genesis 17:1-10. It became the public mark or token of the relation which he sustained to God.
A seal - See the note at John 3:33. A seal is that mark of wax or other substance, which is attached to an instrument of writing, as a deed, etc., to confirm, ratify it, or to make it binding. Sometimes instruments were sealed, or made authentic by stamping on them some word, letter, or device, which had been engraved on silver, or on precious stones. The seal or stamp was often worn as an ornament on the finger; Esther 8:8; Genesis 41:42; Genesis 38:18; Exodus 28:11, Exodus 28:36; Exodus 29:6 To affix the seal, whether of wax, or otherwise, was to confirm contract or an engagement. In allusion to this, circumcision is called a seal of the covenant which God had made with Abraham. That is, he appointed this as a public attestation to the fact that he had previously approved of Abraham, and had made important promises to him.
Which he had, yet being circumcised - He believed Genesis 15:5; was accepted, or justified; was admitted to the favor of God, and favored with clear and remarkable promises Genesis 15:18-21; Genesis 17:1-9, before he was circumcised. Circumcision, therefore, could have contributed neither to his justification, nor to the premises made to him by God.
That he might be the father ... - All this was done that Abraham might be held up as an example, or a model, of the very doctrine which the apostle was defending. The word “father” here is used evidently in a spiritual sense, as denoting that he was the ancestor of all true believers; that he was their model, and example. They are regarded as his children because they are possessed of his spirit; are justified in the same way, and are imitators of his example; see the note at Matthew 1:1. In this sense the expression occurs in Luke 19:9; John 8:33; Galatians 3:7, Galatians 3:29.
Though they be not circumcised - This was stated in opposition to the opinion of the Jews that all ought to be circumcised. As the apostle had shown that Abraham enjoyed the favor of God previous to his being circumcised, that is, without circumcision; so it followed that others might on the same principle also. This instance settles the point; and there is nothing which a Jew can reply to this.
That righteousness ... - That is, in the same way, by faith without works: that they might be accepted, and treated as righteous.