Faithful Abraham. This expression is very emphatic. They are blessed, not with Abraham as circumcised, nor as entitled to boast of the works of the law, nor as a Hebrew, nor as relying on his own excellence, but with Abraham, who by faith alone obtained the blessing; for no personal quality is here taken into the account, but faith alone. The word Blessing is variously employed in Scripture: but here it signifies Adoption into the inheritance of eternal life.

So then they which be of faith - They whose leading characteristic it is that they believe. This was the leading trait in the character of Abraham, and this is the leading thing required of those who embrace the gospel, and in the character of a true Christian.
Are blessed with faithful Abraham - In the same manner they are interested in the promises made to him, and they will be treated as he was. They are justified in the same manner, and admitted to the same privileges on earth and in heaven.

They which be of faith - All who believe, as Abraham has believed, are made partakers of Abraham's blessings.

(9) So then they which be of faith are blessed (g) with faithful Abraham.
(9) The conclusion of the fifth argument: therefore as Abraham is blessed by faith, so are all his children (that is to say, all the Gentiles that believe) blessed, that is to say, freely justified.
(g) With faithful Abraham, and not by faithful Abraham, to show us that the blessing comes not from Abraham, but from him by whom Abraham and all his posterity is blessed.

So then they which be of faith,.... This is the apostle's conclusion upon the whole, from the instance of Abraham, and, the promise made to him; and is an explanation of the preceding clause, and shows that it must be taken in a limited sense, and understood not of every individual; only of those who are of the same faith with Abraham, are believers in Christ, and seek for justification by faith in him, and not by the works of the law:
these are blessed with faithful Abraham; in his seed Christ; they are blessed with a justifying righteousness in Christ as he was, and will be blessed with eternal life as he is; they shall sit with him, and with Isaac and Jacob in the kingdom of heaven. The character of "faithful" given to him, respects not his uprightness and integrity among men, but his faith in God; and does not suppose that he was blessed for his faith, but that it was through faith that he received the blessing of justification, and not by the works of the law; and that in the same way, all that believe enjoy the same favour, for to them it is limited and restrained: nor can the Jews of all men find fault with this interpretation of the apostle's, since they themselves interpret the above clause of some particular persons of the nations of the world, and say in so many words, that
"the meaning is, not that all the men of the world should be blessed, but that every family that is in the world, , "that comes to the obedience and faith of him" (God,) to it shall adhere the blessing and providence. (o)''
(o) Abarbinel in Pentateuch, fol. 54. 1, 2. Vid. R. Isaac Chizzuk Emuna, par. 1. c. 13. p. 135.

they--and they alone.
of faith--(See on Galatians 3:7, beginning).
with--together with.
faithful--implying what it is in which they are "blessed together with him," namely, faith, the prominent feature of his character, and of which the result to all who like him have it, is justification.

So then all they, and they only, who are of faith - Who truly believe. Are blessed with faithful Abraham - Receive the blessing as he did, namely, by faith.