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And you, child, will be called the prophet of the Most High;
For you will go before the Lord to prepare his ways,
77To give knowledge of salvation to his people by the forgiveness of their sins.
78By the tender mercy of our God, the dawn from on high will break upon us,
To give light to those who sit in darkness and in the shadow of death,
To guide our feet into the way of peace.
When John grows up, he will be the penultimate prophet, the final voice before the Voice of God himself is heard among his people once more. He will prepare the way for the glory of the Lord to be revealed in Israel (Isaiah 40.3-5).
How will he do this? His ministry will involve announcing the coming salvation and encouraging the people to seek forgiveness of sins. This, of course, John fulfilled in his ministry of baptism when he gathered people at the Jordan River (the place where Israel first entered the Land) and called them to repentance.
And then the Light of God himself will arise in the darkness that has enveloped the Land. The "the sun of righteousness shall rise, with healing in its wings" (Malachi 4.2), and Isaiah's words will be fulfilled: "The people who walked in darkness have seen a great light; those who lived in a land of deep darkness—on them light has shined." Zechariah's song reflects these and other prophecies that had long awaited fulfillment in Israel.
The result? Peace. Peace on earth, goodwill toward men. An end to enmity with God and between warring factions among men. John will be the final herald calling God's people to ready themselves for the dawning of eternal light and peace.