A difference exists between a furnished and destitute state. The one is of the law considered in itself and its own nature; the other, in relation to us. The law was given to man in the beginning (before the fall) for life and by itself also led to life according to the sanction “do this and thou shalt live” (cf. Rom. 2:13). But after the fall, being destitute of strength through the flesh, it is not given for life, but for a mirror of sin and misery to render the sinner inexcusable (Rom. 3:19, 20). [1.4.15]

…So God seriously wills (i.e., commands man to obey the law that he may live, according to the brief clause of the covenant of works: “Do this and thou shalt live”). [4.17.45]

IV. (2) If Adam was righteous, he ought to have been immortal because there is a necessary connection between righteousness and life. (a) From the order of God who has joined righteousness and life in the law by an indissoluble bond (as he joined closely together sin and death: “Do this and thou shalt live; the soul that sinneth it shall die”). [5.12.4]

XVII. There is not the same relation of justification and of the covenant through all things. To the former, faith alone concurs, but to the observance of the latter other virtues also are required besides faith. These conduce not only to the acceptance of the covenant, but also to its observance. For these two things ought always to be connected—the acceptance of the covenant and the keeping of it when accepted. Faith accepts by a reception of the promises; obedience keeps by a fulfillment of the commands. “Be ye holy, for I am holy.” And yet in this way legal and evangelical obedience are not confounded because the legal is prescribed for the meriting of life, the evangelical, however, only for the possession of it. The former precedes as the cause of life (“Do this and thou shalt live”); the latter follows as its fruit, not that you may live but because you live. The former is not admitted unless it is perfect and absolute; the latter is admitted even if imperfect, provided it be sincere. That is only commanded as man’s duty; this is also promised and given as the gift of God. [12.3.17]

— Francis Turretin, Institutes of Elenctic Theology, trans. George Musgrave Giger, ed. James T. Dennison Jr. (Phillipsburg, NJ: P&R Publishing, 1992–97).