Let them be only thine own - The off-spring of a legitimate connection; a bastard brood, however numerous, is no credit to any man.

Let them be only (i) thine own, and not strangers' with thee.
(i) Distribute them not to the wicked and infidels, but reserve them for yourself, your family and them who are of the household of faith.

Let them be only thine own, and not strangers' with thee. Or "they shall be thine own" (u), as the Targum; meaning not the cistern, the well, or the wife, but the fountains and rivers, or the children; by a man's cleaving to his own wife, who is a chaste and virtuous woman, he is satisfied that the children he has by her are his own, and not another's; whereas if he has to do with a common harlot, it is uncertain whose children they are, she prostituting herself to many: it may be applied to the peculiar possession and steadfast retention of the truths of the Gospel, in opposition to all divers and strange doctrines propagated by others; see Revelation 2:25.
(u) "erunt tui", Mercerus, Cocceius; "erunt tibi", Baynus; "existent tibi", Schultens.

only thine own--harlots' children have no known father.

That such matters as there are thought of, is manifest from this verse. As זרע comprehends with the cause (sperma) the effect (posterity), so, in Proverbs 5:16, with the effusio roboris virilis is connected the idea of the beginnings of life. For the subjects of Proverbs 5:17 are the effusiones seminis named in Proverbs 5:16. These in their effects (Proverbs 5:17) may belong to thee alone, viz., to thee alone (לבדּך, properly in thy separateness) within thy married relation, not, as thou hast fellowship with other women, to different family circles, Aben-Ezra rightly regards as the subject, for he glosses thus: הפלגים שׁהם הבנים הבשׁרים, and Immanuel well explains יהיוּ־לך by יתיחסו לך. The child born out of wedlock belongs not to the father alone, he knows not to whom it belongs; its father must for the sake of his honour deny it before the world. Thus, as Grotius remarks: ibi sere ubi prolem metas. In ואין the יהיו is continued. It is not thus used adverbially for לא, as in the old classic Arabic lyas for l' (Fl.), but it carries in it the force of a verb, so that יהיו, according to rule, in the sense of ולא היו = ולא יהיו, continues it.