Gregory the Great — on Titus 1:16 (Forty Gospel Homilies, Homily 19)

“"For many are called, but few are chosen," because many come to faith, yet few are led to the heavenly kingdom. For behold, how many of us have gathered for today's feast, we fill the walls of the Church, yet who knows how few there are who are numbered in that flock of God's elect? For behold, the voice of all proclaims Christ, but the life of all does not proclaim Him. Most follow God with their voices, but flee from Him by their conduct. Hence Paul says: "They profess to know God, but by their deeds they deny Him." Hence James says: "Faith without works is dead." Hence through the Psalmist the Lord says: "I have declared and spoken, they have multiplied beyond number." For when the Lord calls, the faithful are multiplied beyond number, because sometimes even those come to faith who do not attain to the number of the elect. For here they are mingled with the faithful through confession, but because of their reprobate life they do not deserve to be numbered there in the lot of the faithful.”