Jamieson, Fausset and Brown on Zechariah 3:5

5. And I said--Here the prophet, rejoicing at the change of raiment so far made, interposes to ask for the crowning assurance that the priesthood would be fully restored, namely, the putting the miter or priestly turban on Joshua: its fair color symbolizing the official purity of the order restored. He does not command, but prays; not "Set," but "Let them set." Vulgate and Syriac version read it, "He then said," which is the easier reading; but the very difficulty of the present Hebrew reading makes it less likely to come from a modern corrector of the text.

angel of ... Lord stood by--the Divine Angel had been sitting (the posture of a judge, Da 7:9); now He "stands" to see that Zechariah's prayer be executed, and then to give the charge (Zec 3:6, 7).