The Pulpit Commentary
The case supposed here is that of one professing to have supernatural intelligence, who should, by giving a sign or a wonder, endeavor to draw away the people to idolatry. Such a one was to be put to death.

A prophet (nabhi, נבָיִא); one who speaks from God, an interpreter to men of what God reveals or suggests to him (of. for the meaning of the word, Exo_7:1 with Exo_4:16; also Jer_15:19). Dreamer of dreams. Not by visions or immediate suggestion only, but also by means of dreams, did God communicate with men (cf. Num_12:6). The case supposed here, then, is that of one pretending to have had revelations from God through those media by which God was pleased to convey his will to men (cf. Hem; 'Iliad,' h 62—

"Ἀλλ ἄγε δή τινα μάντιν ἐρείομεν ….

ἢ καὶ ὀνειροπόλον καὶ γάρ τ̓ ὄναρ ἔκ Διός ἐστιν)"

Sign or a wonder. A sign was some event foretold by the prophet, and the occurrence of which was a token that something else which he announced would happen or should be done. A wonder was a miracle, the performance of which gave proof of a Divine commission (cf. Deu_4:24). These signs, it is assumed, should come to pass; nevertheless, the people were not to listen to the man who gave them to go after other gods. The mere fact that he sought to persuade them to forsake the worship of Jehovah was sufficient to prove him an impostor; for how could one who sought to seduce the people from God be sent by God? The sign which was given to authenticate such a message could only be one of those "lying signs and wonders after the working of Satan," by which his emissaries try to deceive and mislead; and was permitted by God only that their fidelity to him might be tested and proved. They had already received God's message; they had his word; and no teaching which contravened that, however apparently authenticated, could be from him, or was to he accepted by them (cf. Jer_29:8; Gal_1:8, Gal_1:9; 1Jn_3:1, etc.). Come what might, they were to walk after Jehovah their God, and keep his commandments, and obey his voice, and serve him; and cleave unto him. The false prophet, as a public enemy and a suborner of treason against the King of Israel, was to be put to death; and so the evil would be put away from among them.

The Pulpit Commentary
A second case supposed is that of temptation to apostasy proceeding from some near relative or intimate friend. Not only was this to be resisted, but no consideration of affection or bend of friendship was to be allowed to interfere with the stern sentence which doomed the tempter to death; on the contrary, the person tempted was to be the first to lay hands on the tempter and put him to death. This was to be done by stoning, and the person he had tried to seduce was to cast the first stone.

Thy brother, the son of thy mother; thy full brother, allied to thee by the closest fraternal tie. The wife of thy Bosom; the object of thy tenderest affection, Whom it is thine to protect and cherish (cf. Deu_28:54, Deu_28:56; Mic_7:5). Thy friend, which is as thine own soul; i.e. whom thou lovest as thyself. The word translated "friend" (רֵעַ, for רֵעֶהֹ) is from a verb which signifies to delight in, and conveys primarily the idea not merely of a companion, but of a friend in whom one delights; and the definition of true friendship is the loving another as one's self (Aristot; 'Eth. Nic.,' Deu_9:5). As commonly used, however, the word designates any one with whom one has any dealing or intercourse; and so our Lord expounds it (Luk_10:29, etc.). Secretly. If the temptation was in private, and so known only to thyself.

The Pulpit Commentary
Pity, spare, conceal. The accumulation of terms serves to make the injunction more solemn and impressive.

The Pulpit Commentary
The penalty publicly inflicted, and therefore generally known, would have a deterrent effect on the community, so as to prevent the recurrence of such evil.

The Pulpit Commentary
A third ease supposed is that of the inhabitants of a city being seduced by wicked men into idolatry. In this case inquiry was to be made as to the fact; and if it was found to be so, the inhabitants of that city were to be put to the sword, all their property was to be burnt, and the city itself reduced to a heap; so should the anger of the Lord be averted from Israel, and he would do them good.

Hear in one of thy cities. The Hebrew phrase, "to hear in" (שָׁמַע בְּ). has sometimes the meaning of to overhear, as in Gen_27:5; 1Sa_17:28; Job_15:8; sometimes it means simply to hear, as in 2Sa_19:36 [35]; in Job_26:14, it has the force of to hear of or concerning, though some think this questionable. This latter is apparently the meaning here: If thou hear concerning any of thy cities, etc. Baying. This introduces what is heard.

The Pulpit Commentary
Men, the children of Belial; the sons of worthlessness, utterly worthless persons. Beli ya‛al (a compound of בְלִי, not, and עָל, to ascend, to have worth, to profit) means primarily that which is low, hence worthlessness, naughtiness, wickedness. In Deu_15:9, Belial is rendered in the Authorized Version as an adjective, "wicked," and also in Neh_1:11. In Psa_18:4, it is rendered by "ungodly men." Most commonly it is treated as a proper name. But in all places the proper meaning of the word might be retained. The Hebrews described an object, of which any quality was predominantly characteristic, as the son of that quality. Are gone out from among you; have gone forth from the midst of you, i.e. have risen up among yourselves. Withdraw. The verb here is the same as that rendered by "thrust," in Psa_18:5 and Psa_18:10. It conveys the idea of drawing away with some degree of force, not mere easy seduction, but impulsion by strong persuasion.

Deu_13:14, Deu_13:15

After due inquiry, if it was found that such a thing had really been done in any of their cities, the extreme penalty was to be inflicted on the city and all its inhabitants—all were to be destroyed. Smite … with the edge of the sword; literally, with the mouth of the sword, as biting and devouring like a ravenous beast—a phrase for utter destruction.

The Pulpit Commentary
All the spoil thereof every whir, for the Lord thy God; rather, all the spoil [booty] thereof as a whole offering unto Jehovah thy God; it was to be wholly devoted to God, and as such to be consumed by fire. "It was a destruction, and not properly an offering. Hence the author selects neither עֹולָה nor חַטָּאת, but כָּליִל, whole, whole offering (Deu_33:10; Le Deu_6:15 [22]), which word, in the law concerning offering, is no technical designation of any particular kind of offering. The rendering omnino is untenable" (Knobel). The city was to be made a ruin, never to be rebuilt; and thus was to be treated the same as a heathen, idolatrous city might be (cf. Num_21:3).