1)
What is "Ash"?
1.
Radak: It [is a moth that] eats garments.
2)
What is "Rekev"?
1.
Rashi: It is a worm that eats wood, and minces it.
3)
How will Hashem be like Ash and Rekev?
1.
Radak: So He will consume Efrayim and Yehudah.
2.
Malbim: The consumption and destruction of Efrayim and Yehudah will not be natural rather, of Hashgachah. I will destroy them like moths and worms that eradicate and decompose everything. Ash comes from the outside, and Rekev from the matter itself that rots. Hashem came to Efrayim from outside, for He did not dwell there rather, in Tziyon. He was in Yehudah, and destroyed it.
