IX. Although faith in Christ is not prescribed specifically and expressly in the law (which does not know Christ), still it is contained in it generically and implicitly (inasmuch as the law commands us to believe every word of God and all his promises). Thus no one could obey the law who was not prepared also to believe the word of the gospel (if it had been revealed by God).
Francis Turretin, Institutes of Elenctic Theology, ed. James T. Dennison Jr., trans. George Musgrave Giger, (Phillipsburg, NJ: P&R Publishing, 1992–97), 8.2.9 (1.573).