For what knowest thou, O woman? Those who are of opinion that this observation is a confirmation of the second department of his statement, expound it thus. "An uncertain hope ought not to detain thee," etc. But, in my opinion, the exhortation is taken from the advantage to be derived; for it is a great and distinguished blessing if a wife gain (1-Corinthians 9:19) her husband. Now, unbelievers are not in so hopeless a condition but that they may be brought to believe. They are dead, it is true, but God can even raise the dead. So long, therefore, as there remains any hope of doing good, and the pious wife knows not but that she may by her holy conversation (1-Peter 3:1) bring back her husband into the way, [1] she ought to try every means before leaving him; for so long as a man's salvation is doubtful, it becomes us to be prepared rather to hope the best. As to his saying, however, that a husband may be saved by his wife, the expression, it is true, is not strictly accurate, as he ascribes to man what belongs to God; but there is no absurdity in it. For as God acts efficaciously by his instruments which he makes use of, he does, in a manner, communicate his power to them, or, at least, he connects it with their service in such a manner, that what he does he speaks of as being done by them, and hence, too, he sometimes ascribes to them the honor which is due to himself alone. Let us, however, bear in mind, that we have nothing in our power, except in so far as we are directed by him as instruments.

Footnotes

1 - "Au bon chemin;" -- "Into the good way."

For what knowest thou - The apostle here assigns a reason why the believing party should not separate from the other needlessly, or why he should not desire to be separated. The reason is, the possibility, or the probability, that the unbelieving party might be converted by the example and entreaties of the other.
Whether then - How do you know "but" this may be done? Is there not a possibility, nay a probability of it, and is not this a sufficient reason for continuing together?
Save thy husband - Gain him over to the Christian faith; be the means of his conversion and salvation. compare Romans 11:26. We learn from this verse:
(1) That there is a possibility that an unbelieving partner in life may be converted by the example of the other.
(2) That this should be an object of intense interest to the Christian husband or wife, because:
(a) It will promote the happiness of the other;
(b) It will promote their usefulness;
(c) It will be the means of blessing their family, for parents should be united on the subject of religion, and in their example and influence in training up their sons and daughters; and,
(d) Because the salvation of a beloved husband or wife should be an object of intense interest,
(3) This object is of so much importance that the Christian should be willing to submit to much, to bear much, and to bear long, in order that it may be accomplished. Paul said that it was desirable even to live with a pagan partner to do it; and so also it is desirable to bear much, very much, with even an unkind and fretful temper, with an unfaithful and even an intemperate husband, or with a perverse and peevish wife, if there is a prospect that they may be converted.
(4) this same direction is elsewhere given; 1-Peter 3:1-2.
(5) it is often done. It is not hopeless. Many a wife has thus been the means of saving a husband; many a husband has been the means of the salvation of the wife - In regard to the means by which this is to be hoped for, we may observe that it is not by a harsh, fretful, complaining temper; it is to be by kindness, and tenderness, and love. It is to be by an exemplification of the excellency of religion by example; by patience when provoked, meekness when injured, love when despised, forbearance when words of harshness and irritation are used, and by showing how a Christian can live, and what is the true nature of religion; by kind and affectionate conversation when alone, when the heart is tender, when calamities visit the family, and when the thoughts are drawn along by the events of Providence toward death. Not by harshness or severity of manner, is the result to be hoped for, but by tender entreaty, and mildness of life, and by prayer. Pre eminently this is to be used. When a husband will not hear, God can hear; when he is angry, morose, or unkind, God is gentle, tender, and kind; and when a husband or a wife turn away from the voice of gentle entreaty, God's ear is open, and God is ready to hear and to bless. Let one thing guide the life. We are never to cease to set a Christian example; never to cease to live as a Christian should live; never to cease to pray fervently to the God of grace, that the partner of our lives may be brought under the full influence of Christian truth, and meet us in the enjoyments of heaven.

For what knowest thou, O wife - You that are Christians, and who have heathen partners, do not give them up because they are such, for you may become the means of saving them unto eternal life. Bear your cross, and look up to God, and he may give your unbelieving husband or wife to your prayers.

For what knowest thou, O wife,.... These words may be understood, as containing a reason either why the believing party should be easy at the departure of the unbeliever, after all proper methods have been used in vain to retain him or her; taken from the uncertainty and improbability of being of any use to them, to bring them to the knowledge of Christ, and salvation by him; "for what knowest thou, O wife"; thou dost not know, thou canst not know, thou canst not be sure,
whether thou shall save thy husband? be the means of bringing of him under the means of grace, and so of his conversion and salvation; there is no likelihood of it, since he is such an implacable enemy to Christ, and so bitterly averse to the Gospel, and the ordinances of it; and therefore since he is determined to separate, even let him go: or else, as rendering a reason why the believer should seek for peace and reconciliation, and by all means, if possible, continue to dwell with the unbeliever; taken from hopes of being serviceable under a divine influence and blessing, for their spiritual and eternal good, the wife for the good of the husband; by whose conversation he may be won over, and prevailed upon to entertain a better opinion of the Christian religion; to take a liking to the Gospel, and to attend upon the ministry of the word, which may be made the power of God unto salvation to him:
or how knowest thou, O man, whether thou shall save thy wife; this may possibly be done, in the same manner as now suggested: persons in such a relation have often great influence upon one another, and are by divine Providence often great blessings to each other, in things spiritual as well as temporal. This puts me in mind of a case related by the Jewish doctors (a):
"it happened to a holy man that he married a holy woman, and they had no children; say they, we are of no manner of profit to the blessed God; they stood up and divorced one another; he went and married a wicked woman, and she made him wicked; she went and married a wicked man, "and she made him righteous";''
or, to use the apostle's phrase, "saved him".
(a) Bereshit Rabba, sect. 17. fol. 14. 4.

What knowest thou but that by staying with thy unbelieving partner thou mayest save him or her? Enforcing the precept to stay with the unbelieving consort (1-Corinthians 7:12-14). So Ruth the Moabitess became a convert to her husband's faith: and Joseph and Moses probably gained over their wives. So conversely the unbelieving husband may be won by the believing wife (1-Peter 3:1) [CALVIN]. Or else (1-Corinthians 7:15), if thy unbelieving consort wishes to depart, let him go, so that thou mayest live "in peace": for thou canst not be sure of converting him, so as to make it obligatory on thee at all costs to stay with him against his will [MENOCHIUS and ALFORD].
save--be the instrument of salvation to (James 5:20).