On temptation

Yet temptations, though troublesome and severe, are often useful to a man, for in them he is humbled, purified, and instructed. The saints all passed through many temptations and trials to profit by them, while those who could not resist became reprobate and fell away. There is no state so holy, no place so secret that temptations and trials will not come. Man is never safe from them as long as he lives, for they come from within us—in sin we were born. When one temptation or trial passes, another comes; we shall always have something to suffer because we have lost the state of original blessedness.
Many people try to escape temptations, only to fall more deeply. We cannot conquer simply by fleeing, but by patience and true humility we become stronger than all our enemies. The man who only shuns temptations outwardly and does not uproot them will make little progress; indeed they will quickly return, more violent than before.

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Above all, we must be especially alert against the beginnings of temptation, for the enemy is more easily conquered if he is refused admittance to the mind and is met beyond the threshold when he knocks. — Thomas Kempis, The Imitation of Christ