Imitation of Christ

Si autem profecutus fuerit quod concupiscitur, statim ex reatu conscientiæ gravatur, quia secutus est passionem suam, quæ nihil juvat ad pacem, quam quæsivit. Resistendo igitur passionibus invenitur vera pax cordis non autem serviendo eis. Non est ergo pax in corde hominis carnalis, non in homine in exterioribus dedito, sed in fervido spirituali. 

But if, on the other hand, he yields to his inclination, immediately he is weighed down by the condemnation of his conscience; for he has followed his own desire, and yet in no way attained the peace which he hoped for. For true peace of heart is to be found in resisting passion, not in yielding to it. And therefore there is no peace in the heart of a man who is carnal, nor in him who is given up to the things that are outside himself, but only in him who is fervent towards living the life of the Spirit.

Imitation of Christ, I, 6:2