A fountain is a source of pure, flowing water used for cleansing and purification (see Zechariah 14:8; John 4:14; Revelation 22:1–2).
God will cleanse Israel, including its leaders (represented by the family line of kings descended from David) and all the people of Judah and Israel (represented by the people of Jerusalem, the nation's spiritual center).
to cleanse them: This cleansing, symbolized by the ceremonial washings in Old Testament worship (see Exodus 30:17–21), was provided in the new covenant as promised by Jeremiah (Jeremiah 31:34) and Ezekiel (Ezekiel 36:25; see Hebrews 10:1–22).
sin and impurity: The Hebrews would experience complete moral and spiritual cleansing because of their sorrow over their sin (Zechariah 12:10–14).