So then they which be of faith are blessed with faithful Abraham ( ὥστε οἱ ἐκ πίστεως εὐλογοῦνται σὺν τῷ πιστῷ ἀβραάμ) "Are blessed;" are objects of benediction. The apostle gathers from the words cited in Galatians 3:8 the two particulars, that there are who get to be blessed like Abraham and with him, and that it is by faith like Abraham's, without works of the Law, that they do so.
He seems to have an eye to the sense of Divine benediction which the Galatians had themselves experienced, when upon their simply believing in Christ the Spirit's gifts had been poured forth upon them.
The word "faithful" ( πιστῷ) is inserted, ex abundanti almost, to mark the more explicitly and emphatically, the condition on which both Abraham and therefore others in him gain the blessing. This being "in Abraham," which is here predicated of all who gain justification and God's benediction, is analogous to the image of Gentiles, being by faith "grafted," and by faith abiding, in the "olive tree," which we have in Romans 11:17, Romans 11:20.
The verbal πιστὸς is generally passive, "one to be believed or trusted in," and so a man "of fidelity;" but it is also at times active, in the sense of "one who believes," as John 20:27; Acts 10:45; 2 Corinthians 6:15; Ephesians 1:1; 1 Timothy 4:10; 1 Timothy 5:16; 1 Timothy 6:2 (so in ἄπιστος, John 20:27; ὀλιγόπιστος, Matthew 6:30).
In consequence of this use of the term in Scripture, both fidelis in ecclesiastical Latin and "faithful" in English have often this signification.