Hence in opposition to that Sinai Law which ran upon those terms Do and Live, under the dispensation of the New, we hear so often of Believe and be saved, and he which believeth have everlasting Life, Mark 16.16.
Joh.3.16, 36. Not that believing now, taketh the place of doing in the Old Covenant; for then it must be our righteousness unto Justification, Gal 3.12. Rom 10.5., whereas that which justifieth is called, the righteousness of Faith, ver.6. and Phil.3.9. and therefore Faith is distinct from that righteousness it self, is not the least Atome of it: therefore, not our believing, but the obedience of Jesus Christ, is that which cometh in the room and stead of that doing for Life intended in the Law.
“Christ and the Condition: Samuel Petto (c.1624-1711) on the Mosaic Covenant,” by Michael G. Brown
The Sovereign Logos 