Nick Norelli refers to John Wesley’s take on this verse, as an Arminian exemplar. I likewise take the time to post John Calvin’s take:
3.But God came to Abimelech in a dream by night. Here Moses shows that the Lord acted with such gentleness, that in punishing his servant, he yet, as a father, forgave him: just as he deals with us, so that, while chastising us with his rod, his mercy and his goodness far exceed his severity. Hence also we infer, that he takes greater care of the pious than carnal sense can understand; since he watches over them while they sleep. This also is to be carefully noticed; that however we may be despised by the worlds we are yet precious to him, since for our sake he reproves even kings, as it is written in Psa_105:14. But as this subject was more fully discussed in the twelfth chapter, (Gen_12:1 ) let the readers there seek what I now purposely omit. Whereas, God is said to have come, this is to be applied to the perception of the king, to whom undoubtedly the majesty of God was manifested; so that he might clearly perceive himself to be divinely reproved and not deluded with a vain spectre.
Behold, thou art but a dead man. Although God reproved king Abimelech, for the sake of Abraham, whom he covered with his special protection; he yet intends to show, generally, his high displeasure against adultery. And, in truth, here is no express mention of Abraham; but rather a general announcement is made, for the purpose of maintaining conjugal fidelity. ‘Thou shalt die, because thou hast seized upon a women who was joined to a husband.’ Let us therefore learn, that a precept was given in these words, to mankind, which forbids any one to touch his neighbor’s wife. And, truly, since nothing in the life of man is more sacred than marriage, it is not to be wondered at, that the Lord should require mutual fidelity to be cherished between husbands and wives and should declare that he will be the Avenger of it, as often as it is violated. He now addresses himself, indeed, only to one man; but the warning ought to sound in the ears of all, that adulterers — although they may exult with impunity for a time — shall yet feel that God, who presides over marriage, will take vengeance on them. (Heb_13:4.)
4.But Abimelech had not come near her. Though Abraham had deprived himself of his wife, the Lord interposed in time to preserve her uninjured. When Moses previously relates, that she was taken away by Pharaoh, he does not say whether her chastity was assailed or not; but since the Lord then also declared himself the vindicator of her whom he now saved from dishonor, we ought not to doubt that her integrity was preserved both times. For why did he now forbid the king of Gerar to touch her, if he had previously suffered her to be corrupted in Egypt? We see, however, that when the Lord so defers his aid as not to stretch out his hand to the faithful, till they are in extreme peril, he shows the more clearly how admirable is his Providence.
Wilt thou slay also a righteous nation?The explanation given by some, that Abimelech here compares himself with the men of Sodom, is perhaps too refined. The following meaning appears to me more simple; namely ‘O Lord, although thou dost severely punish adultery, shall thy wrath pour itself out on unoffending men, who have rather fallen into error, than sinned knowingly and willingly?’ Moreover, Abimelech seems so to clear himself, as if he were entirely free from blame: and yet the Lord both admits and approves his excuse. We must, however, mark in what way, and to what extent he boasts that his heart and hands are guiltless. For he does not arrogate to himself a purity which is altogether spotless; but only denies that he was led by lust, either tyrannically or purposely, to abuse another man’s wife. We know how great is the difference between a crimeand a fault; (429) thus Abimelech does not exempt himself from every kind of charge, but only shows that he had been conscious of no such wickedness as required this severe punishment. The ‘simplicity of heart,’ of which he speaks, is nothing else than that ignorance which stands opposed to consciousness of guilt; and ‘the righteousness of his hands,’ is nothing but that self-government, by which men abstain from force and acts of injustice. Besides, the interrogation which Abimelech used proceeded from a common feeling of religion. For nature itself dictates, that God preserves a just discrimination in inflicting punishments.
6.Yea, I know that thou didst this in the integrity of thy heart. We infer from this answer of God, (as I have lately remarked,) that Abimelech did not testify falsely concerning his own integrity. Yet, while God allows that his excuse is true, He nevertheless chastises him. Let us hence learn, that even they who are pure, according to human judgment, are not entirely free from blame. For no error may be deemed so excusable, as to be without some deteriorating admixture. Wherefores it is not for any one to absolve himself by his own judgment; rather let us learn to bring all our conduct to the standard of God. For Solomon does not say in vain, that ‘the ways of men seem right to themselves,
but the Lord pondereth the hearts,’ (Pro_21:2.)
But if even they who are unconscious to themselves of any evil, do not escape censure; what will be our condition, if we are held inwardly bound by our own conscience?
I also withheld thee. This declaration implies that God had respect, not only to Abraham, but also to the king. For because he had no intention of defiling another man’s wife, God had compassion on him. And it frequently happens, that the Spirit restrains, by his bridle, those who are gliding into error; just as, on the other hand, he drives those headlong, by infatuations and a spirit of stupor, who, with depraved affections and lusts, knowingly transgress. And as God brought to the heathen king, who had not been guilty of deliberate wickedness, a timely remedy, in order that his guilt should not be increased; so He proves himself daily to be the faithful guardian of his own people, to prevent them from rushing forward, from lighter faults to desperate crimes.
7.Now therefore, restore the man his wife. God does not now speak of Abraham as of a common man, but as of one who is so peculiarly dear unto himself, that He undertakes the defense of his conjugal bed, by a kind of privilege. He calls Abraham a prophet, for the sake of honor; as if he were charging Abimelech with having injured a man of great and singular excellence; that he might not wonder at the greatness of the punishment inflicted upon him. And although the word prophet is properly the name of an office; yet I think it has here a more comprehensive import, and that it is put for a chosen man, and one who is familiar with God. For since at that time, no Scripture was in existence, God not only made himself known by dreams and visions but chose also to himself rare and excellent men, to scatter abroad the seed of piety, by which the world would become more inexcusable. But since Abraham is a prophet, he is constituted, as it were, a mediator between God and Abimelech. Christ, even then, was the only Mediator; but this was no reason why some men should not pray for others; especially they who excelled in holiness, and were accepted by God; as the Apostle teaches, that ‘the fervent prayers of a righteous man avail much.’ (Jas_5:16.) And we ought not, at this day, to neglect such intercession, provided it does not obscure the grace of Christ, nor lead us away from Him. …
And if thou restore her not. Hence we are to learn, the intention of those threats and denunciations with which God terrifies men; namely, forcibly to impel those to repentance, who are too backward. In the beginning of this discourse, it had been absolutely declared, ‘Thou art a dead man;’ now the condition is added, ‘Unless thou restore her.’ Yet the meaning of both expressions is the same; though at first God speaks more sharply, that he may inspire the offender with the greater terror. But now, when he is subdued, God expresses his intention more clearly, and leaves him the hope of pardon and salvation. Thus is the knot untied, with which many entangle themselves, when they perceive that God does not always, or instantly, execute the punishments which he has denounced; because they deem it a sign, either that God has changed his purpose, or that he pretends a different thing by his word, from that which he has secretly decreed. He threatens destruction to the Ninevites, by Jonah, and afterwards spared them. (Jon_3:4.) The unskilful do not perceive how they can escape from one of two absurdities; namely, that God has retracted his sentence; or that he had feigned himself to be about to do what he really did not intend. But if we hold fast this principle, that the inculcation of repentance is included in all threats, the difficulty will be solved. For although God, in the first instance, addresses men as lost; and, therefore, penetrates them with the present fear of death, still the end is to be regarded. For if he invites them to repentance, it follows, that the hope of pardon is left them, provided they repent.
Institutes Book 1, Chapter 17:
Who does not now see that, by threatening of this kind, God wished to arouse those to repentance whom he terrified, that they might escape the judgement which their sins deserved? If this is so, the very nature of the case obliges us to supply a tacit condition in a simple denunciation. This is even confirmed by analogous cases. The Lord rebuking King Abimelech for having carried off the wife of Abraham, uses these words: “Behold, thou art but a dead man, for the woman which thou hast taken; for she is a man’s wife.” But, after Abimelech’s excuse, he thus speaks: “Restore the man his wife, for he is a prophet, and he shall pray for thee, and thou shalt live; and if thou restore her not, know thou that thou shalt surely die, thou and all that art thine” (Gen_20:3, Gen_20:7). You see that, by the first announcement, he makes a deep impression on his mind, that he may render him eager to give satisfaction, and that by the second he clearly explains his will. Since the other passages may be similarly explained, you must not infer from them that the Lord derogated in any respect from his former counsel, because he recalled what he had promulgated. When, by denouncing punishment, he admonishes to repentance those whom he wishes to spare, he paves the way for his eternal decree, instead of varying it one whit either in will or in language. The only difference is, that he does not express, in so many syllables, what is easily understood. The words of Isaiah must remain true, “The Lord of hosts has purposed, and who shall disannul it? And his hand is stretched out, and who shall turn it back?” (Isa_14:27).