Malachi 3:1-4 (NRSV): The Coming Messenger
1 See, I am sending my messenger to prepare the way before me, and the Lord whom you seek will suddenly come to his temple. The messenger of the covenant in whom you delight—indeed, he is coming, says the Lord of hosts. 2 But who can endure the day of his coming, and who can stand when he appears? For he is like a refiner’s fire and like fullers’ soap; 3 he will sit as a refiner and purifier of silver, and he will purify the descendants of Levi and refine them like gold and silver, until they present offerings to the Lord in righteousness. 4 Then the offering of Judah and Jerusalem will be pleasing to the Lord as in the days of old and as in former years.

Luke 1:76-79 (NRSV):
76 "And you, child, will be called the prophet of the Most High;
    for you will go before the Lord to prepare his ways,
77 to give knowledge of salvation to his people
    by the forgiveness of their sins.
78 By the tender mercy of our God,
    the dawn from on high will break upon us,
79 to give light to those who sit in darkness and in the shadow of death,
    to guide our feet into the way of peace.”