Or HaChaim on Deuteronomy 13:9/אור החיים על דברים י״ג:ט׳

1ולא תחוס עינך עליו, "and your eye shall not take pity on him;" this means that one has to deny the enticer everything he desires or holds dear, even things totally unrelated to what he proposed. The idea is to make him endure suffering. You should not say that there is no point in making this person endure pointless denials seeing that G'd Himself has permitted all these things to be enjoyed by man. Even though the afflictions we speak about affect primarily the soul, they will also have an effect on the spiritually negative mani-festations which have become an inseparable part of this human being. This is the mystical dimension of the whole concept of fasting. Man is to deny himself food and drink in order to weaken the forces of evil within him.

2ולא תכסה, "and you must not cover up, etc," This may best be understood by a reference to Kidushin 81 in which the Talmud relates a story involving Rav Amram. [The subject matter is being alone with a woman who is not your wife and the implications of such a situation. Ed.] Certain female prisoners whose freedom had been bought by the people of Nehardea, the town in which the pious Rav Amram resided, were entrusted to him for safekeeping. He assigned to them the top floor, removing the connecting stairs. One day he was sorely tempted by his evil urge to socialise with one or the other of these women and he single-handedly put up a ladder to climb the upper floor which it would normally require several people to move. When half way up he cried out that his house was on fire which brought out the neighbours before he could succumb totally to the enticer within him. He embarassed himself thereby publicly, but told his colleagues that it was better for him to be embarassed in the here and now, than to face the consequences of his action in the hereafter where his embarassment would be far greater. Moses says here that you should not conceal the fact that the enticer is active within you, but by exposing this fact similar to Rav Amram, you will be able to defeat the enticer by publicly disgracing him for what he is. כי הרוג תהרגנו, "Rather, you must surely kill him."

3Moses adds: ידך תהיה בו בראשונה להמיתו, "your hand shall be the first against him to kill him." Moses indicates that in contrast to what Rav Amram did in the story related in Kidushin when he called on others to killl the evil urge within himself, you must do so yourself, at least you must begin the job. Only if you failed in your attempt may you do as Rav Amram did, i.e. call upon outsiders to do what is really your task. Only when you are in the position described by David in Psalms 109,22 that "my heart is pierced within me," may you call on G'd to do the job on your behalf as did David in Psalms 109,26, i.e. "Help me O Lord my G'd, etc." If you fail by yourself, Moses' final comment i.e. ויד כל העם באחרונה "and the hand of all the people at the end," applies. This is a reference to the situation when you may do as Rav Amram did and call in outside help.