I have created a PBB resource of J. Gresham Machen’s book, The Origin of Paul’s Religion. You can download it by clicking on the attachment link below.
Machen taught at Princeton Theological Seminary from 1915 to 1929 and was the last of the “great” Princeton theologians, including B.B. Warfield and Charles Hodge. Machen was a contemporary of the prolific Geerhardus Vos, who also taught at Princeton.