Rashi: The gifts that I legislated for them, to sanctify every Bechor for Me, I handed them over to their Yetzer to pass their Bechoros to Molech. These are bad Chukim!

Radak: This refers to when Nitzmedu l'Va'al Pe'or - they made a tight connection to it. They passed every firstborn, which I commanded to take for Me for Kedushah - "Kadesh Li Kol Bechor" (Shemos 13:2) - and passed them from Me and gave them to idolatry. Their Tum'ah was opposite Kedushah! I made them Tamei, and distanced them from Me, in place of what I sanctified them. Since they did not want that, I made them Tamei and distanced them from Me. The Shevet (Shimon) that clung to Ba'al Pe'or, Moshe did not mention it in his Brachos to the Shevatim.

Malbim: They think that I was not Mekadesh them, rather, I was Metamei them via their gifts. I commanded to bring every firstborn to Hashem. They were used to serving the sun; they designated the firstborn to be Kadosh for Avodas ha'Molech (the sun). My command to sanctify every Bechor to Me, and not offer it to idolatry, was Tum'ah for them, as of they left their Kedushah. My Mitzvos to benefit, sustain and sanctify them, they considered to be for their evil, to kill and be Metamei them. They called good evil, and evil good.

Rashi: It is an expression of Shemamah ¹ - I will make them desolate. Radak - it should say Ashimemem. (There is a Dagesh in the first Mem in place of the missing Mem. - PF)

Radak: I warned them that if they transgress My Mitzvos, they will be desolate. They did the opposite of My will, in order that I make them desolate! The desolation was right next to their sin - 24,000 died.

Malbim: The Galuyos that I will impose on them will have two purposes. (a) To make them desolate due to their sin. (b) So they will know that I am Hashem. They will return to Me in the end of days.

Rashi: When I bring the evil on them.