Purity, we see in the object-lesson, is not the one thing needful; and it is better that a life should contract many a dirt-mark, than forfeit usefulness in its efforts to remain unspotted.
 William James, The Varieties of Religious Experience (1902). copy citation

Context

“But when the intellect, as in this Louis, is originally no larger than a pin's head, and cherishes ideas of God of corresponding smallness, the result, notwithstanding the heroism put forth, is on the whole repulsive. Purity, we see in the object-lesson, is not the one thing needful; and it is better that a life should contract many a dirt-mark, than forfeit usefulness in its efforts to remain unspotted. [pg 355] Proceeding onwards in our search of religious extravagance, we next come upon excesses of Tenderness and Charity. Here saintliness has to face the charge of preserving the unfit, and breeding parasites and beggars.” source