The Imitation of Christ, by Thomas a Kempis, tr. by William Benham , at sacred-texts.com
Whensoever a man desireth aught above measure, immediately he becometh restless. The proud and the avaricious man are never at rest; while the poor and lowly of heart abide in the multitude of peace. The man who is not yet wholly dead to self, is soon tempted, and is overcome in small and trifling matters. It is hard for him who is weak in spirit, and still in part carnal and inclined to the pleasures of sense, to withdraw himself altogether from earthly desires. And therefore, when he withdraweth himself from these, he is often sad, and easily angered too if any oppose his will.
2. But if, on the other hand, he yield to his inclination, immediately he is weighed down by the condemnation of his conscience; for that he hath 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 without him, but only in him who is fervent towards God and living the life of the Spirit.