If he has declared himself opposed to sin and unrighteousness, then sin and unrighteousness will be rooted out of human history. God will not fail. No one will ever laugh at him. No one will ever point at God's declared intentions and describe him as a failure. Whatever a man sows, this he will also reap.
Nobody gets away with anything.
That is the heart of what Zechariah is trying to say to us. God's word triumphs. He speaks and it comes to pass. We need to be people who not only have the highest theological and prophetic view of scripture, but people who also recognize in our daily walk, in the choices we make, whether or not we want to obey God's word. We need to recognize the unfailing quality of the word of God.