Thou art my sister - Thou art my dearest friend, and I will treat thee as such.

Say unto wisdom, Thou art my sister,.... Intimately acquainted, greatly beloved, and highly delighted in: this may be understood both of the Gospel, the wisdom of God in a mystery, which men should be conversant with, be strongly affected to, and take delight and pleasure in; and of Christ, the essential Wisdom of God, and who stands in the relation of a brother to his people, and should be respected as such;
and call understanding thy kinswoman; or "kinsman" (a); such Christ is in our nature, our "goel", our near kinsman, partaker of the same flesh and blood, and therefore is not ashamed to call us brethren, nor should we be ashamed to call him kinsman: moreover, his Word and Gospel, and the understanding of it, should be familiar to us; it should be well "known" (b) by us, as the word used signifies, and dwell richly in us.
(a) "cognatum", Piscator. (b) "Notam", Montanus, Michaelis.

The subject-matter of this earnest warning are the admonitions of the teacher of wisdom, and through him of Wisdom herself, who in contrast to the world and its lust is the worthiest object of love, and deserves to be loved with the purest, sincerest love:
4 Say to wisdom: "Thou art my sister!"
And call understanding "Friend;"
5 That they may keep thee from the strange woman,
From the stranger who useth smooth words.
The childlike, sisterly, and friendly relationship serves also to picture forth and designate the intimate confidential relationship to natures and things which are not flesh and blood. If in Arabic the poor is called the brother of poverty, the trustworthy the brother of trustworthiness, and abu, um (אם), achu, ucht, are used in manifold ways as the expression for the interchangeable relation between two ideas; so (as also, notwithstanding Ewald, 273b, in many Hebr. proper names) that has there become national, which here, as at Job 17:14; Job 30:29, mediated by the connection of the thoughts, only first appears as a poetic venture. The figurative words of Proverbs 7:4 not merely lead us to think of wisdom as a personal existence of a higher order, but by this representation it is itself brought so near, that אם easily substitutes itself, Proverbs 2:3, in the place of אם. אחתי of Solomon's address to the bride brought home is in its connection compared with Book of Wisdom 8:2. While the ôth of אחות by no means arises from abstr. ûth, but achôth is derived from achajath, מודע (as Ruth 2:1, cf. מודעת, Proverbs 3:2), here by Mugrash מודע, properly means acquaintance, and then the person known, but not in the superficial sense in which this word and the Arab. ma'arfat are used (e.g., in the Arabic phrase quoted by Fleischer, kanna aṣḥaab ṣarna m'aaraf - nous tions amis, nous en sommes plus que de simples connaissances), but in the sense of familiar, confidential alliance. The infin. לשׁמרך does not need for its explanation some intermediate thought to be introduced: quod eo conducet tibi ut (Mich.), but connects itself immediately as the purpose: bind wisdom to thyself and thyself to wisdom thus closely that thou mayest therewith guard thyself. As for the rest, vid., Proverbs 2:16; this verse repeats itself here with the variation of one word.

And call - Acquaint and delight thyself with her.