"and in a wasteland, howling and desolate": These are the four exiles, viz. (Devarim 8:15) "Who led you in the great, awesome desert of snake (1), serpent (2), scorpion (3) and waterless drought (4)."
"He surrounded them": with the elders. "He guarded them like the pupil of His eye": He protected them from harm by mazzikim (adverse elements), viz. (Zechariah 2:12) "For he that touches you touches the pupil of His eye."
(Devarim, Ibid. 11) "As an eagle wakes its nest": Just as an eagle does not enter its nest immediately until it flutters its wings between one tree and another, between one booth and another, until its young awake and have the strength to mount it, so, when the L-rd revealed Himself to give the Torah to Israel, He did not reveal Himself to them (suddenly) from one side, but from four, as it is written (Ibid. 33:2) "The L-rd came from Sinai and shone forth from Seir to them. He appeared from Mount Paran." And which is the fourth side? (Habakkuk 3:3) "G-d came from Teman."