IV. (2) Before the fall, he had the power to love God and obey him in all things; for love supposes faith, a part of obedience. For he who is commanded by law to love God and obey him is also commanded to believe him when he speaks. Nor is the exception of force that the power to believe God differs from the power to believe Christ because the word of the law and of the gospel are opposed in their total genus; and in the law he was indeed commanded to love and obey God, but only by reason of the state in which he was constituted by creation (that he should worship his Creator), not in which he was to be restored by redemption (that he should believe in him). Although as to the peculiar formula the law and gospel differ from each other, yet they agree in this: that they are equally the word of God and so the object of our faith and the rule of obedience. Hence he who is bound to believe God speaking in the law and has strength sufficient for it, also is able and ought to believe the gospel (if it is revealed to him). Nor can a greater love or obedience be conceived than that which is enjoined upon us in the law.
Francis Turretin, Institutes of Elenctic Theology, ed. James T. Dennison Jr., trans. George Musgrave Giger, vol. 1 (Phillipsburg, NJ: P&R Publishing, 1992–97), 8.2.4 (pp. 572–73).