And seest - a beautiful woman - No forcible possession was allowed even in this case, when the woman was taken in war, and was, by the general consent of ancient nations, adjudged as a part of the spoils. The person to whose lot or share such a woman as is here described fell, might, if he chose, have her for a wife on certain conditions; but he was not permitted to use her under any inferior character.

And seest among the captives a beautiful woman,.... Whether a virgin, wife, or widow, according to the Jewish writers, even though another man's wife; so Jarchi (c), and Maimonides (d); the marriages of Gentiles being reckoned by the Jews no marriages:
and hast a desire unto her; being captivated with her beauty; some understand this of the strength and rage of lust, but it rather signifies a passionate desire of enjoying her in a lawful way, as follows:
that thou wouldest have her to thy wife; to be married to her in a legal manner; for though it was not allowed the Israelites to marry any of the seven nations of Canaan, nor indeed with any of other nations continuing in their idolatry; yet they might marry such as became their captives and servants, and were wholly in their own power; and especially if proselytes to their religion, and which this fair captive was to become before marriage, as is by some gathered from the following things to be done by her; though after all, this was only a permission, because of the hardness of their hearts, as is said of divorce; and that such marriages were not very grateful to God appears, as some have observed, from the ceremonies used before marriage, to render her contemptible; and the easy dismission of her afterwards, according to the sense of some interpreters.
(c) Vid. T. Bab. Kiddushin, fol. 21. 2. (d) Hilchot Melachim, c. 8. sect. 3.

Hast a desire unto her - Or, hast taken delight in her: which may be a modest expression for lying with her, and seems probable, because it is said, Deuteronomy 21:14, that he had humbled her. And here seem to be two cases supposed, and direction given what to do in both of them, that he did desire to marry her, of which he speaks, Deuteronomy 21:11-13. that he did not desire this, of which he speaks, Deuteronomy 21:14.