Not all those who have faith in some way have sufficient fervor and vigor in faith to be willing to relinquish everything. Many, indeed, are unwilling to renounce even the things that are unlawful! For this reason, it is not inappropriate to compare the Kingdom of heaven–that is, the Church–to a net. Once it has been cast into the sea of this world, it draws to the shore–that is, to the end or goal of life–both good and evil together under the confession of a single faith and a single profession of the name “Christian.”
In the Church there are both good and bad, all of whom have faith. There are those who have it profitably and there are those who have it to their detriment. Those who have it to their detriment are those who have recognized the truth, but do not stand in the truth and are turned back on themselves. As Peter says in his Second Epistle: It would have been better for them never to have known the way of righteousness than after recognizing it, to turn back from the holy commandment delivered to them.
from The Commendation of Faith by Baldwin of Forde, CF 59, p. 175