Jamieson, Fausset and Brown on Habakkuk 3:4

4. as the light--namely, of the sun (Job 37:21; Pr 4:18).

horns--the emblem of power wielded by "His hand" [Ludovicus De Dieu]. "Rays" emanating from "His hand," compared by the Arabs to the horns of the gazelle (compare "hind of the morning," Psa 22:1, title, Margin). The Hebrew verb for to "emit rays," is from the root meaning "horns" (Ex 34:29, 30, 35) [Grotius]. The rays are His lightnings (Psa 18:8), [Maurer].

there--in that "brightness." In it, notwithstanding its brilliancy, there was but the veil "(the hiding) of His power." Even "light," God's "garment," covers, instead of revealing fully, His surpassing glory (Psa 104:2) [Henderson]. Or, on Mount Sinai [Drusius]. (Compare Ex 24:17). The Septuagint and Syriac versions read for "there," He made a hiding, &c.; He hid Himself with clouds. English Version is better, which Calvin explains, there is said to be "a hiding of God's power," because God did not reveal it indiscriminately to all, but specially to His people (Psa 31:20). The contrast seems to me to be between the "horns" or emanations out of His power ("hand"), and that "power" itself. The latter was hidden, whereas the "horns" or emanations alone were manifested. If the mere scintillations were so awfully overwhelming, how much more so the hidden power itself! This was especially true of His manifestation at Sinai (Psa 18:11; compare Is 45:15, 17).