XXV. Such a perfect observance of the laws of the covenant, up to the period which God had fixed for probation, had given man a right to the reward. Not from any intrinsic proportion of the work to the reward, as the grosser Papists proudly boast; but from God’s covenant and engagement, which was no ways unbecoming him to enter into. Nor had man, before the consummation of his obedience, even in the state of innocence, a right to life. He was only in a state of acquiring a right, which would at length be actually acquired, when he could say, I could have fulfilled the conditions of the covenant, I have constantly and perfectly done what was commanded; now I claim and expect that thou, my God, wilt grant the promised happiness.
XXVI. How absurdly again do the Papists assert, that Adam, as he came from the hands of his Creator, had a right, as the adopted Son of God, to supernatural happiness, as to his paternal inheritance; which, according to Bellarmine, de Justificat. l. v. 17. “is due to the adopted Son of God, in right of adoption, previous to all good works.” But this is truly a preposterous way of reasoning. For the right of adoption belongs to the covenant of grace in Christ Jesus: “the adoption of children is by Jesus Christ,” Eph. 1:5. Besides, was this opinion true, good works could not be required, as the condition of acquiring a right to eternal life; but could only serve to prevent the forfeiture of the right of a son: by this means, the whole design of the covenant of works, and all the righteousness which is by the law, are quite destroyed. In fine, what can be more absurd, than the trifling manner in which these sophisters talk of the grace of adoption, as giving Adam a right to enter upon an heavenly inheritance, in a legal covenant: when, on the other hand, they so stiffly contend for the merits of works, under a covenant of grace. It is only there (to wit, under the covenant of grace) that we are to apply the above sentiment, that the inheritance is due to an adopted Son of God, in right of adoption, previous to all good works.
—Herman Witsius, The Economy of the Covenants between God and Man: Comprehending a Complete Body of Divinity, trans. William Crookshank, vol. 1 (London: T. Tegg & Son, 1837), vol. 1. pp. 70-71.