ייִדישער מחשבֿה אויף בראשית 46:29

You must know that in Hebrew the collective noun denoting animals used for riding is “mercabah.” Instances of this noun are not rare. “And Joseph made ready his chariot” (merkabto) (Gen. 46:29); “in the second chariot” (be-mirkebet) (ib. 41:43); “Pharaoh’s chariots” (markebot) (Exod. 15:4). The following passage especially proves that the Hebrew merkabah denotes a collection of animals: “And a merkabah came up and went out of Egypt for six hundred shekels of silver, and a horse for an hundred and fifty” (1 Kings 10:21). Hence we may learn that mercabah denotes here four horses. Therefore I think that when it was stated, according to the literal sense of the words, that four Ḥayyot (beasts) carry the Throne of Glory, our Sages called this “mercabah” on account of its similarity with the mercabah consisting of four single animals.