Albert Barnes Commentary Job 39:28

"On the cliff she dwelleth, and maketh her home, Upon the point of the cliff, and the stronghold." — Job 39:28 (ASV)

She dwelleth and abideth on the rock - "He rarely quits the mountains to descend into the plains. Each pair live in an insulated state, establishing their quarters on some high and precipitous cliff, at a respectful distance from others of the same species" (Edin. Ency.). They seem to occupy the same cliff, or place of abode, during their lives; and for this reason, they are represented as having a permanent abode on the lofty rock.

In Damir it is said that the blind poet Besar, son of Jazidi, upon being asked what he would choose to be if God gave him the choice of being an animal, replied that he would wish to be nothing else than an "alokab," a species of the eagle, because they lived in places to which no wild animal could gain access (Scheutzer, "Phys. Sac." in loc.). The word rendered "abideth" commonly means "to pass the night," and here refers to the fact that the high rock was its constant abode or dwelling. By night as well as by day, the eagle had its home there.

Upon the crag of the rock - Hebrew, "Upon the tooth of the rock" - from the resemblance of the crag of a rock to a tooth.