Verse 12: And Saul was (1 Sam. 18:15, 29) afraid of David, because (1 Sam. 16:13, 18) the LORD was with him, and was (1 Sam. 16:14; 28:15) departed from Saul.
[And Saul was afraid] Lest David should be chosen by the people as king, from a collation of what follows, and from verse 7 (Piscator). Now, in what manner he wished to shake off his fear? he greatly honored him (Martyr).
Saul was afraid of David, lest as he had gotten the favour of God and of all the people, he should also take away his kingdom.
Verse 13: Therefore Saul removed him from him, and made him his captain over a thousand; and (1 Sam. 18:16; Num. 27:17; 2 Sam. 5:2) he went out and came in before the people.
[He removed from himself] David had withdrawn from court, as we said; but he had recalled him, perhaps because he was thinking himself to be otherwise able to satisfy the people’s wishes and affection towards David (Sanchez).
[He made him a tribune] Indeed, with an appearance of honor. But Saul desired something else, 1. That he might free himself from danger, lest David should run him through alone in a private chamber. 2. So that he might appear to stand to his promises. 3. And principally, so that David might be removed from his presence (Martyr). 4. Lest at court he attract the favor of the courtiers to himself (Lapide).
From him; from his presence and court; which he did, partly, because he feared lest David should watch and find an opportunity to kill him, as he had designed to kill David; partly, because he was a great eyesore, and his presence now made him more sad than ever his music had made him cheerful; and principally, that hereby he might expose him to the greatest hazards, and in some sort betray him into the hands of the Philistines.
[He was going out and coming in] To come in and go out is to act as a Captain, and to take charge with power (Menochius, similarly Junius, Piscator, Malvenda). See Numbers 27:17; Deuteronomy 31:2, I can no more go out, etc.; Acts 1:21, He went in and out among us. This denotes free and consummate power, whereby one administrates things by his own will (Sanchez). He was leading the people out to war, and was leading them back, as Generals are wont to do (Vatablus).
He went out and came in; he led his soldiers forth to battle, and brought them back again with safety. Compare 2 Samuel 5:2. Or else the phrase of coming in and going out may be understood (as elsewhere) for conversing; or (as we use to say) going toand fro about business, as 1 Samuel 29:6.
David behaved himself wisely, etc.: So that he had great prudence in his conduct, and prosperous success following his designs; which are two principal qualifications of a general and of a prince. Thus God turned all Saul’s devices upon himself, and to David’s advantage.
Verse 15: Wherefore when Saul saw that he behaved himself very wisely, he was afraid of him.
[He saw that he was prudent, and he began to beware of him] An ill conscience is the cruelest torturer, and it fears all things. The prudence and prosperity of David ought rather to have refreshed the soul of Saul: but he drew poison from the medicine; and he thought that prudence and strength, which were laboring for his welfare and glory, and that of the people, to be armed against himself (Sanchez).
Verse 16: But (1 Sam. 18:5) all Israel and Judah loved David, because he went out and came in before them.
Verse 17: And Saul said to David, Behold my elder daughter Merab, (1 Sam. 17:25) her will I give thee to wife: only be thou valiant (Heb. a son of valour) for me, and fight (Num. 32:20, 27, 29; 1 Sam. 25:28) the LORD’S battles. For Saul said, (1 Sam. 18:21, 25; 2 Sam. 12:9) Let not mine hand be upon him, but let the hand of the Philistines be upon him.
[Behold my elder daughter Merab] Whom he had promised to him previously, 1 Samuel 17:25 (Menochius). He promised, but he did not fulfill: either because he promised falsely, or because he repented of it: for he feared that through his daughter he might advance to the kingdom (Lapide).
Her will I give thee to wife: this was no more than Saul was obliged to do by his former promise, 1 Samuel 17:25, which here he renews and pretends to perform, though he intended nothing less, as the sequel shows; whereby he makes himself guilty of ingratitude, injustice, and breach of trust, and withal of gross hypocrisy.
[Only be to me a mighty man] It is a Hebraism: With this condition, that thou be a Captain and General of my army (Vatablus). לְבֶן־חַיִל, a son of activity; that is, active and strong; or a son of the army, troops; that is, warlike (Malvenda).
[And fight the Lord’s battles] That is, the battles of the Israelite people to uphold the honor of Jehovah against idolatrous Gentiles (Piscator).
[Let not my hand be upon him] It is a Hebraism. Let me not kill him (Vatablus); lest I bring upon myself disgrace and the indignation of the people (Lapide).
[But…the hand of the Philistines] See the malignity and cunning of the envy of Saul, who ever descends to the worse (Lapide). But Saul falls into the pit that he had made for David. For he himself is killed by the Philistines (Martyr on verse 20).
Let the hand of the Philistines be upon him; he thought so great an offer would oblige him, who was of himself valiant enough to give proofs of more than common valour, and to venture upon the most dangerous enterprises.
Verse 18: And David said unto Saul, (see 1 Sam. 18:23; 9:21; 2 Sam. 7:18) Who am I? and what is my life, or my father’s family in Israel, that I should be son in law to the king?
[Who am I? etc.] That is to say, How unimportant am I, and of an abject condition? (Piscator). But David remembered that he was anointed king, and that this was due to him by covenant. Nevertheless, he speaks and feels about himself as one lowly, as Abraham, Paul, and other saints are wont to do (Martyr). David was not thinking the family of Saul to be less noble than his own; nor a herdsman (of which sort was David) to be very different from keeper of asses (of which sort Saul had been formerly): Only he was so averse to exacting the reward promised by Saul to the victor, that he frankly refused the thing voluntarily offered (Sanchez). Marvelous humility and modesty shine forth here (Lapide).
[Or what is my life? וּמִ֣י חַיַּ֔י] That is, what is the manner of my state or condition? (Piscator). Who is the author of my life? (Junius and Tremellius). I would prefer that the word author be not supplemented: but let it be employed to express the trope. The sense: What is the origin of my life? that is, of what sort are my progenitors? In the Hebrew, there is an anomaly of number: for the pronoun is singular; but the noun is plural: as if you should say in Greek, τίς αἱ ζωαί μου, what is my lives? (Piscator).
My life, that is, my manner of living. How obscure is that condition in which I was born, and have been bred! Or rather thus, How little is my life worth, that by the exposing of that to some hazard (which Saul required of him), I should purchase a king’s daughter! In these expressions David showeth not only his humility, but also his wisdom, in discovering so deep a sense of his own meanness, that Saul might see how far he was from aspiring at the kingdom, and might have no occasion to suspect that he was already anointed thereto.
Verse 19: But it came to pass at the time when Merab Saul’s daughter should have been given to David, that she was given unto (2 Sam. 21:8) Adriel the (Judg. 7:22) Meholathite to wife.
When Merab should have been given to David; when the marriage was even ready to be solemnized.
[She was given to Adriel] In a singular injustice, and perfidy; since he wrested away the bride owed by the right of war, and offered voluntarily so many time, not now from the hope of marriage, but almost from the very embrace of the bridegroom. On account of a similar injury Samson burned crops, vineyards, etc., Judges 15. But David, with his sorrow prudently suppressed, and with the injury dissembled, transferred vengeance to the one God. Which He exacted in His own time. See 2 Samuel 21: 8, 9 (Tirinus).
Adriel the Meholathite, the son of Barzillai, as he is called, 2 Samuel 21:8. This was an act of great injustice and perfidiousness; and accordingly this marriage was accursed by God, and the children begotten in it were by God’s appointment cut off, 2 Samuel 21.
 Hebrew: וַיִּרָ֥א שָׁא֖וּל מִלִּפְנֵ֣י דָוִ֑ד כִּֽי־הָיָ֤ה יְהוָה֙ עִמּ֔וֹ וּמֵעִ֥ם שָׁא֖וּל סָֽר׃  Hebrew: וַיְסִרֵ֤הוּ שָׁאוּל֙ מֵֽעִמּ֔וֹ וַיְשִׂמֵ֥הוּ ל֖וֹ שַׂר־אָ֑לֶף וַיֵּצֵ֥א וַיָּבֹ֖א לִפְנֵ֥י הָעָֽם׃  Hebrew: וַיְהִ֥י דָוִ֛ד לְכָל־דָּרְכָ֖ו מַשְׂכִּ֑יל וַֽיהוָ֖ה עִמּֽוֹ׃  Hebrew: מַשְׂכִּיל.  1 Samuel 18:5: “And David went out whithersoever Saul sent him, and behaved himself wisely (יַשְׂכִּיל, prospered): and Saul set him over the men of war, and he was accepted in the sight of all the people, and also in the sight of Saul’s servants.”  Hebrew: וַיַּ֣רְא שָׁא֔וּל אֲשֶׁר־ה֖וּא מַשְׂכִּ֣יל מְאֹ֑ד וַיָּ֖גָר מִפָּנָֽיו׃  See Proverbs 28:1.  Hebrew: וְכָל־יִשְׂרָאֵל֙ וִיהוּדָ֔ה אֹהֵ֖ב אֶת־דָּוִ֑ד כִּֽי־ה֛וּא יוֹצֵ֥א וָבָ֖א לִפְנֵיהֶֽם׃  Hebrew: וַיֹּ֙אמֶר שָׁא֜וּל אֶל־דָּוִ֗ד הִנֵּה֩ בִתִּ֙י הַגְּדוֹלָ֤ה מֵרַב֙ אֹתָהּ֙ אֶתֶּן־לְךָ֣ לְאִשָּׁ֔ה אַ֚ךְ הֱיֵה־לִּ֣י לְבֶן־חַ֔יִל וְהִלָּחֵ֖ם מִלְחֲמ֣וֹת יְהוָ֑ה וְשָׁא֣וּל אָמַ֗ר אַל־תְּהִ֤י יָדִי֙ בּ֔וֹ וּתְהִי־ב֖וֹ יַד־פְּלִשְׁתִּֽים׃  Hebrew: לְבֶן־חַיִל.  Hebrew: אַ֚ךְ הֱיֵה־לִּ֣י לְבֶן־חַ֔יִל.  Hebrew: אַל־תְּהִ֤י יָדִי֙ בּ֔וֹ.  See 1 Samuel 31.  Hebrew: וַיֹּ֙אמֶר דָּוִ֜ד אֶל־שָׁא֗וּל מִ֤י אָֽנֹכִי֙ וּמִ֣י חַיַּ֔י מִשְׁפַּ֥חַת אָבִ֖י בְּיִשְׂרָאֵ֑ל כִּֽי־אֶהְיֶ֥ה חָתָ֖ן לַמֶּֽלֶךְ׃  Hebrew: וַיְהִ֗י בְּעֵ֥ת תֵּ֛ת אֶת־מֵרַ֥ב בַּת־שָׁא֖וּל לְדָוִ֑ד וְהִ֧יא נִתְּנָ֛ה לְעַדְרִיאֵ֥ל הַמְּחֹלָתִ֖י לְאִשָּֽׁה׃