By the experience of active love. Strive to love your neighbour actively and indefatigably. In as far as you advance in love you will grow surer of the reality of God and of the immortality of your soul. If you attain to perfect self-forgetfulness in the love of your neighbour, then you will believe without doubt, and no doubt can possibly enter your soul. This has been tried. This is certain.
I know you'll probably get angry with me for that, shout, stamp your feet: "speak just for yourself and your miseries in the underground, and don't go saying 'we all.'" Excuse me, gentleman, but I am not justifying myself with this allishness. As far as I myself am concerned, I have merely carried to an extreme in my life what you have not dared to carry even halfway, and, what's more, you've taken your cowardice for good sense, and found comfort in thus deceiving yourselves. So that I, perhaps, come out even more "living" than you.
Through error you come to the truth! I am a man because I err! You never reach any truth without making fourteen mistakes and very likely a hundred and fourteen.
Nothing could be more absurd than moral lessons at such a moment! Oh, self-satisfied people: with what proud self-satisfaction such babblers are ready to utter their pronouncements! If they only knew to what degree I myself understand all the loathsomeness of my present condition, they wouldn't have the heart to teach me.
Do you believe in a future everlasting life? No, not in a future everlasting but in an everlasting life here. There are moments, you reach moments, and time comes to a sudden stop, and it will become eternal.
For the secret of man's being is not only to live but to have something to live for. Without a stable conception of the object of life, man would not consent to go on living, and would rather destroy himself than remain on earth, though he had bread in abundance.
Above all, avoid falsehood, every kind of falsehood, especially falseness to yourself. Watch over your own deceitfulness and look into it every hour, every minute.
Above all, don't lie to yourself. The man who lies to himself and listens to his own lie comes to a point that he cannot distinguish the truth within him, or around him, and so loses all respect for himself and for others. And having no respect he ceases to love.
Atheism: It seeks to replace in itself the moral power of religion, in order to appease the spiritual thirst of parched humanity and save it; not by Christ, but by force.
Believe to the end, even if all men went astray and you were left the only one faithful; bring your offering even then and praise God in your loneliness.