Zechariah 13:1

In that day God would open a fountain for the complete spiritual cleansing of the Israelites, both for their moral sins and for their ritual uncleanness (cf. Ezekiel 47). The figure of a fountain pictures abundant cleansing that would continue indefinitely. This will be the fulfillment of God’s promise to forgive the sins of His people Israel in the New Covenant (Zechariah 3:4; Zechariah 3:9; Jeremiah 31:34; Ezekiel 36:25; cf. Romans 11:26-27). "The blood of Jesus . . . cleanses us from all sin" (1 John 1:7). The cleansing is available now, but God will cleanse multitudes of Israelites in the future, after they turn to their Messiah in faith (Zechariah 12:10-14).

"The problem of sin is the central problem in the OT. It began in the garden of Eden and will not be eradicated until the final day of Yahweh." [Note: Smith, p. 280.]