Zechariah 13:1 (ESV) … “On that day there shall be a fountain opened for the house of David and the inhabitants of Jerusalem, to cleanse them from sin and uncleanness.”
Zechariah says that we need cleansing, and he does not leave us in suspense about the nature of the cleansing that he has in mind. It is cleansing ‘for sin and for uncleanness’ (v. 1).
Sin is the worst kind of filth there is. How few are serious about this serious thing! What is sin? It is failing to conform to the laws of God. It is the creature thumbing his nose at the Creator and saying, ‘I will not walk in your way! I will go my own way.’ It is refusing to do those things that God has explicitly commanded, choosing rather to do those things that God has plainly forbidden.
Why is sin so serious? Because it insults the God who has made us and blessed us, and this God is both holy and mighty. His holiness means that he must pronounce judgement upon sin, and his mightiness means that he has the power to bring upon us the judgement that he pronounces. What is the judgement that the holy God has pronounced upon our sin? It is nothing less than eternal separation from him and all that is good and glorious (2 Thes. 1:9).
Sin is defilement of the deepest dye. No soap can remove it. No launderer can expunge it. It requires special cleansing, and, wonder of wonders, the very God who is so profoundly offended by our sin has provided cleansing for it.[1]
[1] Ellsworth, R. (2010). Opening Up Zechariah (pp. 125–126). Leominster: Day One Publications.