וַיָּבֹאוּ֮ אֶל־מַחֲנֵ֣ה יִשְׂרָאֵל֒ וַיָּקֻ֤מוּ יִשְׂרָאֵל֙ וַיַּכּ֣וּ אֶת־מוֹאָ֔ב וַיָּנֻ֖סוּ מִפְּנֵיהֶ֑ם ויבו־[וַיַּכּוּ־] בָ֔הּ וְהַכּ֖וֹת אֶת־מוֹאָֽב׃
And when they came to the camp of Israel, the Israelites rose up and smote the Moabites, so that they fled before them. And they smote the land, even Moab, mightily.
Rashi
והותר is an infinitive similar to, (Exodus 8:11) “[But when Pharaoh saw that there was respite] he allowed his heart to be hardened (והכבד)”; (2 Kings 3:24) “and they smote (והכות) Moab” (infinitives used in perfect sense).
Rashi
והכבד את לבו HE ALLOWED HIS HEART TO BE HARDENED — The word הַכְבֵּד expresses doing something (the Hebrew infinitive but having a past meaning) just as, (Genesis 12:9) “going (הלוך) and journeying (ונסוע)”. So, too, (2 Kings 3:24) “and smiting (והכת) Moab”; (I Samuel 22:13) “and enquiring (ושאול) of God for him”; (1 Kings 20:37); “smiting (הכה) and wounding (ופצוע)”.
Rashi
והקל מעליך lit., AND TO LIGHTEN the burden FROM OFF YOU — this thing will serve to lighten it from off you. והקל — the grammatical form is similar to (Exodus 8:11) ”and to harden (והכבד) his heart”; (2 Kings 3:24) “and to smite (והכות) Moab” — both of which words are infinitives expressing present time.