“Hear now with regard to the stones which are in the building. Those square white stones which fitted exactly into each other, are apostles, bishops, teachers, and deacons, who have lived in godly purity, and have acted as bishops and teachers and deacons chastely and reverently to the elect of God. Some of them have fallen asleep, and some still remain alive. And they have always agreed with each other, and been at peace among themselves, and listened to each other. On account of this, they join exactly into the building of the tower.”
“But who are the stones that were dragged from the depths, and which were laid into the building and fitted in with the rest of the stones previously placed in the tower?” “They are those who suffered for the Lord's sake.” “But I wish to know, O Lady, who are the other stones which were carried from the land.” “Those,” she said, “which go into the building without being polished, are those whom God has approved of, for they walked in the straight ways of the Lord and practiced His commandments.”
“But who are those who are in the act of being brought and placed in the building?” “They are those who are young in faith and are faithful. But they are admonished by the angels to do good, for no iniquity has been found in them.” “Who then are those whom they rejected and cast away?” “These are they who have sinned, and wish to repent. On this account they have not been thrown far from the tower, because they will yet be useful in the building, if they repent. Those then who are to repent, if they do repent, will be strong in faith, if they now repent while the tower is building. For if the building be finished, there will not be more room for any one, but he will be rejected. This privilege, however, will belong only to him who has now been placed near the tower.”
Source: The Pastor (or "The Shepherd") (New Advent)