A man's ethical behaviour should be based effectually on sympathy, education, and social ties and needs; no religious basis is necessary. Man would indeed be in a poor way if he had to be restrained by fear of punishment and hope of reward after death.
At the same time, as social beings, we are moved in the relations with our fellow beings by such feelings as sympathy, pride, hate, need for power, pity, and so on.
We find nothing easier than being wise, patient, superior. We drip with the oil of forbearance and sympathy, we are absurdly just, we forgive everything. For that very reason we ought to discipline ourselves a little; for that very reason we ought to cultivate a little emotion, a little emotional vice, from time to time. It may be hard for us; and among ourselves we may perhaps laugh at the appearance we thus present. But what of that! We no longer have any other mode of self-overcoming available to us: this is our asceticism, our penance.