40 Besides, we ought certainly to note the fact that the evangelical and Scriptures do not confine this designation of His “”disciples to those twelve alone, but give the same appellation to all those who believed on Him, and were educated under His instruction for the kingdom of heaven. Out of the whole number of such He chose twelve, whom He also named apostles, as Luke mentions. For a little further on he says: And He came down with them, and stood in the plain, and the concourse of His disciples and a great multitude of people. And surely he would not speak of a “concourse” [or “crowd”] of disciples if he referred only to twelve men. In other passages of the Scriptures also the fact is plainly apparent, that all those were called His disciples who were instructed by Him in what pertained to eternal life.
Source: The Harmony of the Gospels (New Advent)