IV. This double covenant is proposed to us in Scripture: of nature and of grace; of works and of faith; legal and evangelical. The foundation of this distinction rests both on the different relation (σχέσει) of God contracting (who can be considered now as Creator and Lord, then as Redeemer and Father) and on the diverse condition of man (who may be viewed either as a perfect or as a fallen creature); also on the diverse mode of obtaining life and happiness (either by proper obedience or by another’s imputed); finally on the diverse duties prescribed to man (to wit, works or faith). For in the former, God as Creator demands perfect obedience from innocent man with the promise of life and eternal happiness; but in the latter, God as Father promises salvation in Christ to the fallen man under the condition of faith. The former rests upon the work of man; the latter upon the grace of God alone. The former upon a just Creator; the latter upon a merciful Redeemer. The former was made with innocent man without a mediator; the latter was made with fallen man by the intervention of a mediator.
Francis Turretin, Institutes of Elenctic Theology, ed. James T. Dennison Jr., trans. George Musgrave Giger, vol. 1 (Phillipsburg, NJ: P&R Publishing, 1992–97), 8.3.4 (p. 575, modified according to the 1679 edition).