What does Zechariah 3:9 mean?

Look at the stone I’ve set in front of Joshua! There are seven eyes on this one stone, and I’m going to engrave an inscription on it, says the Lord of all, and I’ll remove this land’s guilt in a single day. Zechariah 3:9 - Modern Text Bible

(The stone with seven eyes is a symbol of God’s watchfulness and purpose. God will deal with the people’s guilt all at once—total forgiveness is coming.)