v1: The vision of Joshua the high priest, with Satan, the accuser, seeking to destroy the Lord's people. Here are developments behind the scenes, unseen from the earth, unknown by the people. Elsewhere, Satan is called the accuser of the brethren (Rev 12.11); this is one of his most powerful weapons against the people of God.
v2: The Lord has chosen Jerusalem, and no enemy accusation can change that. The Angel has no power of himself to rebuke Satan, but the Lord has. Ultimately, Satan cannot stop God's will being fulfilled. Joshua is a firebrand, compare Amos 4.11.
v3-5: Joshua has no goodness in himself. Here is justification by grace, the removal of the filth of the natural man, and the imputing of righteousness; this is totally the work of God.
Joshua spoke no words to Satan, his accuser. He had no words, no argument. He rested in the promises of God, to freely justify him.
v6-7: Joshua has been made righteous, and now has the responsibility to walk in obedience.
v8-9: Joshua and his companions, symbolic of things to come, pointing to the Branch, even Christ. He will remove the iniquity of the land, just as He has removed Joshua's iniquity; Ezek 36.25; Joel 3.21; Zeph 3.11.
v10: Peace in the Lord's reign, previously experienced in 1 Kings 4.25; prophesied also in Mic 4.4; and sought by Nathaniel in John 1.48-50.