The following two paragraphs come from Part I, Chapter VII of Samuel Rutherford's "The Covenant of Life Opened," which was published in 1655.
Rutherford is demonstrating the flaw in the Roman Catholic notion of merit. In doing so, he appeals to the late great Thomas Bradwardine (1290-1349), whose De Causa Dei influenced the theology of John Wycliffe on grace and predestination.
Bradwardine's criticism of merit is that it is too late for it to have any value. For man to have the ability to merit anything with God, man must be the first actor. We know this is false, hence merit is an impossibility.
"The proper work of merit (saith great Bradwardine) and of him that works must go before the wages, in time, or in order of nature. And if the worker receive its operation, and working for wages from God first, and by his virtue and help continue in operation and working, he cannot condignly merit at the hand of God, but is rather more in Gods debt, after his working, then before his working, because he bountifully receives more good from God, then before, especially, because he gives nothing proper of his own to God, but gives to God his own good; But no man first acts for God, for God is the first actor and mover in every action, and motion. As that saith, Who gave first to the Lord, and it shall be recompensed him?
"...God did more to Adam in giving to him being, faculties, mind, will, affections, power, habits, his blessed-Image, then Adam can never be in a condition, in which he can recompense God, or give him more annual and usury, in his acting of obedience, then the stock was he received in proportion. As the Son can never give the Father, in recompense, so much or the captive ransomed from death, can never give to his ransom- payer, who bought him, so much, as the one and the other shall no more be under an obligation, and debt of love and service to father and ransomer, then to a stranger that they never knew: Nor could Adam thus be freed of God, so as he should be owing nothing to him. If any say, God may freely forgive all this obligation and debt: To which Bradwardine answers well: 1. The forgiving of the debt, when the debtor hath nothing to pay is a greater debt taken on. 2. God (saith he) may forgive so in regard of actual obligation, that he is not obliged ad aliquid faciendum sub poena peccati, to do anything under the pain or punishment of sin, as the hireling is obliged to work, when he hath made a Covenant to work, and so we are not obliged to do, as much as we can for God. But in regard of habitual obligation, God cannot forgive the debt, that the reasonable creature owes to God, for so he might dispense with this, that the reasonable creature owe no obedience to God, suppose he should command it, which is impossible."
Samuel Rutherford, The Covenant of Life Opened