Why does it say that their wings are straight?
Rashi: They are in line with each other.
Malbim: Now it explains how the influence comes via the Raki'a from the world above. They receive the influence via their wings, which hint to flying. Their wings do not rest on the side, like birds' wings. Rather, they stand up straight, to under the Raki'a to receive influence from there. The wings were in pairs. One hints to receiving influence from above, and one hints to influencing below. They are conduits for spilling influence.
What do we learn from "Ishah El Achosah"?
Malbim: They are intertwined. The influencer and recipient face each other, like the Keruvim did when Yisrael did Hashem's will.
What do we learn from "l'Ish Shetayim
Radak: There are two for each [Chayah, to cover its body, and two for flying]. Malbim - covering shows concealment. They had two kinds of grasping - how to receive influence from Olam ha'Kisei, and how to bring it down. For each, one wing covered it.
