Tertullian

Nay, but this whole world is the one house of all; in which world it is more the heathen, who is found in darkness, whom the grace of God enlightens, than the Christian, who is already in God's light. Finally, it is one "straying" which is ascribed to the ewe and the drachma: (and this is an evidence in my favour); for if the parables had been composed with a view to a Christian sinner, after the loss of his faith, a second loss and restoration of them would have been noted.