Luke 3 … the word of God came to John the son of Zacharias in the wilderness. And he went into all the region around the Jordan, preaching a baptism of repentance for the remission of sins, as it is written in the book of the words of Isaiah the prophet, saying:“The voice of one crying in the wilderness:
‘Prepare the way of the Lord;
Make His paths straight.
Every valley shall be filled
And every mountain and hill brought low;
The crooked places shall be made straight
And the rough ways smooth;
And all flesh shall see the salvation of God.’”Then he said to the multitudes that came out to be baptized by him, “Brood of vipers! Who warned you to flee from the wrath to come? Therefore bear fruits worthy of repentance, and do not begin to say to yourselves, ‘We have Abraham as our father.’ For I say to you that God is able to raise up children to Abraham from these stones. And even now the ax is laid to the root of the trees. Therefore every tree which does not bear good fruit is cut down and thrown into the fire.”10 So the people asked him, saying, “What shall we do then?”11 He answered and said to them, “He who has two tunics, let him give to him who has none; and he who has food, let him do likewise.”

John cries in the desert because he brings the glad tidings of redemption to deserted and forsaken Judæa, but what he cries is explained in the words, Prepare ye the way of the Lord. For they who preach true faith and good works, what else do they than prepare the way for the Lord’s coming into the hearts of the hearers, that they might make the paths of God straight, forming pure thoughts in the mind by the word of good preaching.

( St. Gregory)