The Conferences Of John Cassian by John Cassian
Chapter VI. How the weak are easily moved.
For those who are not yet settled in the line which they have taken up are often, when they hear some praised for different interests and virtues, so excited by the praise of them that they try forthwith to imitate their method: and in this human weakness is sure to expend its efforts to no purpose. For it is an impossibility for one and the same man to excel at once in all those good deeds which I enumerated above. And if anyone is anxious equally to affect them all, he is quite sure to come to this; viz., that while he pursues them all, he will not thoroughly succeed in any one, and will lose more than he will gain from this changing and shifting about. For in many ways men advance towards God, and so each man should complete that one which he has once fixed upon, never changing the course of his purpose, so that he may be perfect in whatever line of life his may be.