Zechariah 13:1

In that day The day, or period, so often mentioned before (Zechariah 12:3-4; Zechariah 12:6; Zechariah 12:8-9; Zechariah 12:11), in which this whole prophecy shall be fulfilled.

a fountain opened … for sin and for uncleanness The form of the promise is Jewish, the substance Christian. For the lustral waters of the Law, the "water of sin" (Numbers 8:7) and the "water of uncleanness" (Numbers 19:9, where the word is the same as here, though rendered, "water of separation," A. V. and R. V.), which were contained and renewed in bowl or laver, and which did but "sanctify to the purifying of the flesh," shall be substituted the living fountain of the Gospel, opened once but remaining open ever (comp. θύρα ἠνεῳγμένη Revelation 4:1), which "purges the conscience from dead works to serve the living God." (Hebrews 9:13-14; 1 John 1:7.)