Verse 8: (Deut. 17:18, 19) This book of the law shall not depart out of thy mouth; but (Ps. 1:2) thou shalt meditate therein day and night, that thou mayest observe to do according to all that is written therein: for then thou shalt make thy way prosperous, and then thou shalt have good success (or, do wisely, Josh. 1:7).
[Let not the volume of this Law depart] Concerning which, see Deuteronomy 31:9 (Malvenda). Of Deuteronomy, or of the Pentateuch (Lapide). ה/that denotes the book of the Laws of Moses κατ᾽ ἐξοχὴν, preeminently (Masius).
[From thy mouth, etc.] Not that He committed to him the care of teaching and explaining the Law, but this is explained by what follows, but to meditate, etc. For הָגָה is to handle the mind in reflection on those matters in such a way that out of its boiling over, as it were, words also rise up into the mouth, which sort those that rehearse are wont to mutter (Masius). Or, from thy mouth indicates that he is always to speak concerning that. Which הָגָה also signifies. Hence, in Psalm 1:2, Aquila translates הָגָה, to meditate, as φθέγγομαι, to utter (Drusius). If it depart not from the mouth, neither should it from the heart; for out of the heart the mouth speaks, Matthew 12:34 (Serarius).
[But thou shalt meditate] He shows that reading is not sufficiently useful, unless it be considered with much study and meditation in the soul (Masius).
[Day and night] It is Proverbial, as in Homer, —νύκτας τε καὶ ἤματα πάντα, throughout the night and the day. Turn over the pages with a nocturnal hand; turn over the pages with a diurnal hand (Drusius); that is, frequently, diligently, continually (Lapide): at any time it might be able to be performed conveniently and opportunely. Wherefore, not sufficiently judiciously did Rabbi Ishmael, when asked by a certain one, whether it is lawful for him to read the writings of the Greeks, etc., respond, Is there any hour that does not pertain either to the day or to the night? For it is lawful to spend that hour alone on studies other than of the Divine Law (Masius). Truly this study is required of the Prince with good reason, whose faults are far more hurtful (Bonfrerius). Princes, as they excel the others in dignity, so also ought they to excel them in this study; so that they might prove to be the best, and instruct others by their example, and lest they err from the right in their function (Masius).
Shall not depart out of thy mouth, that is, thou shalt constantly read it, and upon occasion discourse of it, and the sentence which shall come out of thy mouth shall in all things be given according to this rule. Meditate therein, that is, diligently study, and frequently and upon all occasions consider what is God’s will and thy duty. The greatness of thy place and employments shall not hinder thee from this work, because this is the only rule of all thy private actions and public administrations.
[That thou mayest keep and do] See verse 7. It teaches that without this reading is not useful, etc. Hence the Talmudists, He that reads the Sacred books, but does not apply it to the situation, is like unto a woman that often bears, but continually buries her offspring (Masius).
According to all that is written therein; whereby he teacheth him that it is his duty to see with his own eyes, and to understand the mind and law of God himself, and not blindly to follow what any other should advise him to.
[Then thou shalt direct thy way, כִּי־אָ֛ז תַּצְלִ֥יחַ אֶת־דְּרָכֶ֖ךָ]] Thou shalt prosper thy way (Vatablus, Masius), or, thou shalt prosper in thy ways (Junius and Tremellius, Vatablus), so that the אֶת might be in the place of ב/in (Vatablus, similarly Montanus, Septuagint, Jonathan, Syriac, Arabic), that is, in the actions of thy life (Lapide).
[And thou shalt understand, וְאָ֥ז תַּשְׂכִּֽיל׃] Thou shalt prosper (Junius and Tremellius); thou shalt be prudent (Masius). Note that here prudence is conjoined with prosperity, as a mother with a daughter (Lapide).
 Hebrew: לֹא־יָמ֡וּשׁ סֵפֶר֩ הַתּוֹרָ֙ה הַזֶּ֜ה מִפִּ֗יךָ וְהָגִ֤יתָ בּוֹ֙ יוֹמָ֣ם וָלַ֔יְלָה לְמַ֙עַן֙ תִּשְׁמֹ֣ר לַעֲשׂ֔וֹת כְּכָל־הַכָּת֖וּב בּ֑וֹ כִּי־אָ֛ז תַּצְלִ֥יחַ אֶת־דְּרָכֶ֖ךָ וְאָ֥ז תַּשְׂכִּֽיל׃
 Hebrew: תַּשְׂכִּיל.
 Hebrew: לֹֽא־יָמ֡וּשׁ סֵפֶר֩ הַתּוֹרָ֙ה הַזֶּ֜ה.
 הָגָה can signify articulate speech, to muse or meditate, or inarticulate speech, to moan or mutter.
 Aquila of Sinope produced his Greek version of the Old Testament in the second century of the Christian era. Aquila’s translation champions the cause of Judaism against Christianity in matters of translation and interpretation. The product is woodenly literalistic.
 Psalm 1:2: “But his delight is in the law of the Lord; and in his law doth he meditate (יֶהְגֶּה) day and night.”
 See, for example, Odyssey 24:63.
 Horace’s Art of Poetry 269.
 Rabbi Ishmael (c. 90-135) was a Tannaic sage. His teaching and example, as recorded in the Mishnah, are designed to promote peace among men. Rabbi Ishmael is most remembered for his system of halakhic exegesis, providing guidance on the logical derivation of one law from another, while at the same time staying close and remaining true to the express statements of Scripture.
 Hebrew: לְמַ֙עַן֙ תִּשְׁמֹ֣ר לַעֲשׂ֔וֹת.
 Joshua 1:7a: “Only be thou strong and very courageous, that thou mayest observe to do (לִשְׁמֹ֤ר לַעֲשׂוֹת֙) according to all the law, which Moses my servant commanded thee…”
 צָלֵחַ signifies to advance, or to prosper.
 The Direct Object marker.
 שָׂכַל, in the Qal, signifies to be prudent; in the Hiphil, to act prudently, or to prosper.