1)
Why does the Navi elaborate to describe the Keruvim?
1.
Rashi: Because one of the Chayos' faces was changed 1 , it needed to repeat their description, lest one say that it is a different Merkavah.
2.
Malbim: He was shown that also in conduct that overrides the Ma'arachah, the Ofanim are tied to the Keruvim. Above (1:15-17) I explained the four Ofanim.
1
These are the Chayos of above (15). Rashi (1) - they are called Keruvim, for one face turned into a Keruv.
