Joshua’s filthy garments were exchanged for a clean outfit, signifying what God was doing for his sins. This is how the blood of Christ works for all of us, cleansing us from our iniquities. 2 Corinthians says Christ took our filthy sins upon Himself to clothe us with His righteousness.
The next picture, with its poor resolution, for which I apologize, has our comrade Patriarch standing with Joshua who fought the battle of Jericho. Is this the same Joshua about which Zechariah is speaking?