Prepare ye the ways of the Lord, make His paths straight. LK 3:4
John, being chosen for the Apostleship, was also the last of the holy prophets: for which reason, as the Lord was not yet come, he says, Prepare ye the way of the Lord. And what is the meaning of “Prepare ye the way of the Lord?” It is put for, Make ready for the reception of whatever Christ may wish to enact: withdraw your hearts from the shadow of the law: cease from the types: think no more perversely. “Make the paths of our God straight.” For every path that leadeth unto good is straight and smooth and easy: but the other is crooked that leadeth down to wickedness them that walk therein. For of such it is written, “Whose paths are crooked, and the tracks of their wheels awry.” Straightforwardness therefore of the mind is as it were a straight path, having no crookedness. Such was the divine Psalmist’s character, who thus sings, “A crooked heart hath not cleaved unto me.” And Jesus, the son of Nun, in exhorting the people, said, “Make straight your hearts unto the God of Israel:” while John cries, “Make straight your ways.” And this means, that the soul must be straight, displaying its natural intuition as it was created: and it was created beautiful and very straight. But when it turns aside, and its natural state is perverted, this is called vice, and the perversion of the soul.
The matter therefore is not very difficult: for if we continue as we are made, we shall be virtuous.But when someone, as it were, exclaims against us, saying, How shall we prepare the way of the Lord? or how make His paths straight? for there are many impediments in the way of those that will live well,—-Satan, who hates all that is beautiful, the unholy throng of wicked spirits, the law of sin itself that is in our fleshly members, and which arms itself against the inclinations of the mind to what is good, and many other passions besides, that have mastery over the mind of man:—-what then shall we do, with so great difficulty pressing upon us? The word of prophecy meets these objections, saying, “Every valley shall be filled up, and every mountain and hill shall be brought low: and the crooked way shall become straight, and the rough ways shall become smooth: and all flesh shall see the salvation of God.”
St. Cyril of Alexandria, Commentary on Luke, Homily 6.