So then they which be of faith are blessed with faithful Abraham.
They - and they alone.
Of faith - (note, Galatians 3:7.)
With - together with. As "IN" regards Abraham as the spiritual father in whom, so "with" regards him as one with whom all believers shall be blessed (Matthew 8:11).
Faithful - the point in which they are 'blessed together with him'-namely, faith, his prominent characteristic, of which the result is justification.