Conversion to Christianity During the First Centuries; Author: Gustave Bardy

The same procedure of individual action is found from the origin of the Church; and perhaps this has been the way through which during the centuries Christianity conquered most of its faithful. Every believer is necessarily an apostle:

from the moment he has found the truth, he has no rest or truce until he makes his family members, his friends, his co-workers participate in his happiness.

From the Eucharist to the Trinity, Author: M. V. Bernadot

The Christian is a sower of joy; and for this he does great things. Joy is one of the most irresistible powers in the world: calms, disarms, conquers, drags. The happy soul is an apostle: it draws men to God, manifesting to them what the presence of God produces in them. This is why the Holy Spirit gives us this advice: never be afflicted, because joy in God is your strength (Nehemiah 8, 10)