Jamieson, Fausset and Brown on Daniel 7:9

9. I beheld till--I continued looking till.

thrones ... cast down--rather, "thrones were placed" [Vulgate and Luther], namely, for the saints and elect angels to whom "judgment is given" (Da 7:22), as assessors with the Judge. Compare Da 7:10, "thousand thousands ministered unto Him" (Mt 19:28; Lu 22:30; 1Co 6:2, 3; 1Ti 5:21; Re 2:26; 4:4). In English Version the thrones cast down are those of the previously mentioned kings who give place to Messiah.

Ancient of days--"The everlasting Father" (Is 9:6). He is the Judge here, as THE Son does not judge in His own cause, and it is His cause which is the one at issue with Antichrist.

sit--the attitude of a judge about to pass sentence.

white--The judicial purity of the Judge, and of all things round Him, is hereby expressed (Re 1:14).

wheels--as Oriental thrones move on wheels. Like the rapid flame, God's judgments are most swift in falling where He wills them (Eze 1:15, 16). The judgment here is not the last judgment, for then there will be no beast, and heaven and earth shall have passed away; but it is that on Antichrist (the last development of the fourth kingdom), typical of the last judgment: Christ coming to substitute the millennial kingdom of glory for that of the cross (Re 17:12-14; 19:15-21; 11:15).