Deuteronomy 20:18

Deu 20:18. That they teach you not to do after all their abominations — Here is the great reason for the aforesaid severe execution; they were most abominable idolaters, who offered their children to Moloch; they were magicians, wizards, necromancers, and guilty of all those abominations and filthy lusts mentioned Leviticus 18. So that God thought them not fit to live any longer upon the face of the earth; for had they been spared, after obstinately rejecting terms of peace, they would undoubtedly have sought to infect the Israelites with their filthy idolatry; and it was mercy to the human race in general not to suffer such a wicked, contagious generation to subsist. From the words here quoted, That they teach you not, &c., a Jewish writer justly observes, “If they repented and forsook their idolatry, the Israelites might let them live;” for then there was no such danger in sparing them. Accordingly Rahab, her father, mother, brethren, and all her kindred, were preserved alive, and so were the Hivites or Gibeonites, on condition of servitude, which they themselves offered, Jos 9:11-15. See Jos 11:11-20; Jer 18:7-8.

Joseph Benson's Commentary on the Old and New Testaments (1811–1818) — public domain. Text from a community e-Sword module.

18. The one Pl. passage in this law, see introd. note.

abominations] See on Deu_7:25, Deu_12:31, Deu_17:1.

19 f. Of Sparing the Fruit Trees in a Siege

In a prolonged siege, Israel, while eating of the besieged’s fruit-trees, shall not destroy them (Deu_20:19). Trees which do not yield food may be cut down for siege-works (Deu_20:20).—In the Sg. address.

The practice of cutting down the enemy’s fruit trees was common. Several Assyrian kings boast of it: cp. Tiglath Pileser iii. (quoted in E.B. 4512): ‘The plantations of palms which abutted on his rampart I cut down.’ Both Pompey and Titus cleared away the trees round Jerusalem, the latter for a distance of 90 stadia (Josephus VI. B.J. i. 1, viii. 1, v. B.J. iii. 2). Mohammed destroyed the palms of the Banu Nadir, and justified this in an oracle, Ḳuran lix. See also Doughty Ar. Des. i. 23.

On invading Moab Israel cut down the fruit-trees and stopped the wells, in obedience to a word of Jehovah by Elisha (2Ki_3:19; 2Ki_3:25). That prophet, therefore, and his biographer cannot have known of this law of D, which shows a real advance in the ethics of warfare.—Further on Sieges see O. C. Whitehouse art. ‘Siege’ in E.B.; Billerbeck, Festungsbau im Alten Orient.

The Cambridge Bible for Schools and Colleges (gen. ed. J. J. S. Perowne; Cambridge University Press, 1878–1918) — public domain. Text from a community e-Sword module.

That they teach you not to do after all their abominations,.... This is another reason why they were to be utterly destroyed, not only because of the abominations which they committed, but to prevent the Israelites being taught by them to do the same; wherefore, as before observed from Jarchi, such as became proselytes were suffered to live among them, because there was no danger of idolatry from them, which even proselytes of the gate renounced; and though all other abominations are included, yet this is particularly respected, as appears from the following clause:

which they have done unto their gods; to the honour of whom not only many superstitious rites and ceremonies were performed, and idolatrous actions committed, but acts of lewdness, and even unnatural uncleanness:

so should ye sin against the Lord your God; a sin the most provoking to him, as the sin of idolatry was; and cause his anger to rise to such a degree, as to suffer them to be carried captive from the land he gave them to inherit; and which afterwards, was the case, and that through learning the manners and customs of these people; see Psa 106:34.

John Gill's Exposition of the Whole Bible (1746–1763) — public domain (CC PDM 1.0). Text via the HelloAO Bible API.

למען אשר לא ילמדו [BUT THOU SHALT DOOM THEM TO DESTRUCTION …] THAT THEY TEACH YOU NOT TO DO [AFTER THEIR ABOMINATIONS] — Consequently if they repent of their abominations and wish to become proselytes you are allowed to accept them as such (Sifrei Devarim 202:1).

Rashi on the Tanakh — English translations: “The Judaica Press complete Tanach with Rashi, translated by A. J. Rosenberg” (CC BY 4.0); “Pentateuch with Rashi's commentary by M. Rosenbaum and A.M. Silbermann, 1929-1934” (public domain); “The Metsudah Tanach series, Lakewood, N.J” (CC BY 4.0); and “The Book of Joshua, Metsudah Publications, 1997” (CC BY 4.0). Text via Sefaria.

THAT THEY TEACH YOU NOT TO DO AFTER ALL THEIR ABOMINATIONS, WHICH THEY HAVE DONE UNTO THEIR GODS. The purport thereof is that they will teach you to worship the Glorious Name with the burning of your sons and daughters and every abomination to the Eternal, which He hateth, and so ye sin against the Eternal your G-d Who has warned you against saying, How used these nations to serve their gods? even so will I do likewise. Now the Torah warned them, They shall not dwell in thy Land, lest they make thee sin against Me, for thou wilt serve their gods, for they will be a snare unto thee, which is an admonition against idolatry, for if you make a covenant with them and their gods, they will dwell in your Land and many of them will entice you to worship the idols. He added here to explain that thou shalt save alive nothing that breatheth, for even one of them that remains among you to serve you, will remind you of the worship of their gods and perhaps you will be persuaded to do so to the Glorious Name and you will sin against Him, blessed be He.

Ramban (Nachmanides) on the Tanakh — English translation: “Commentary on the Torah by Ramban (Nachmanides). Translated and annotated by Charles B. Chavel. New York, Shilo Pub. House, 1971-1976” (CC BY 4.0). Text via Sefaria.