To Stay Purehearted

Marcus Aurelius in Book VIII, Section L, of Meditations, on staying purehearted:

"They kill me. They cut my flesh. They persecute my person with curses." What then? May not thy mind for all this continue pure, prudent, temperate, just? As a fountain of sweet and clear water, though she be cursed by some stander by, yet do her springs nevertheless still run as sweet and clear as before; yea though either dirt or dung be thrown in, yet is it no sooner thrown, than dispersed; and she cleared. She cannot be dyed or infected by it. What then must I do, that I may have within my self an overflowing fountain, and not a well? Beget thyself by continual pains and endeavours to true liberty with charity, and true simplicity and modesty.