Albert Barnes Commentary Psalms 68:33

"To him that rideth upon the heaven of heavens, which are of old; Lo, he uttereth his voice, a mighty voice." — Psalms 68:33 (ASV)

To him that rideth upon the heavens of heavens - The highest heavens. The heaven of heavens would properly mean the heaven above that which is heaven to us; that is, the heaven above the sky. This is represented as the special dwelling-place of God. The Jews were accustomed to speak of three heavens:

1. The aerial heaven, or the region above us, where the birds fly, and the winds blow;
2. the starry heavens, or the firmament in which the stars are fixed; and
3. the heaven above all, the abode of God and of angels.

The word “rideth” here means that he appears there as a conqueror, or that he moves in majesty and glory. See the notes at (Psalms 18:10).

Which were of old - The words “of old” refer here to the heavens, and denote their antiquity. He rides upon those ancient heavens. He occupies a position above those ancient works of his power.

Lo, he doth send out his voice - Margin, as in Hebrew, “give.” The reference is to thunder. The design of this is to increase the impression of his majesty and power.

And that a mighty voice - See the notes at (Psalms 29:3).