Friedrich Nietzsche, answered from the texts and cited to the page.
The death of God is not an event that happened one morning in a church. It is the long consequence of Christianity's own most rigorous instinct: the will to truth.1 Christianity trained Europe to be honest, to demand truthfulness as a supreme value — and that demand, turned at last upon Christian doctrine itself, found the doctrine insupportable.
"God is truth" becomes, through the very seriousness Christianity taught, "all is false." The executioner of God is God's own morality.2 What collapses with God is not merely a metaphysical proposition but an entire architecture of value. Morality, which had borrowed its sanction from the divine order, no longer knows how to maintain itself.3
The whole European system of striving feels itself partly meaningless, partly immoral — and this is what I call nihilism: not a mood, not social distress, not physiological decay, but the final logical consequence of the values we have lived by.4 Nihilism is not the cause of anything; it is the result of taking our highest values seriously enough to watch them dissolve.
The danger is therefore not that people will become wicked. The danger is that they will sense the collapse only dully — feel a vague unease, a romantic pessimism, a yearning for nothingness — without understanding what has actually occurred.5 Most will reach for substitutes: socialism, science, nationalism, a new Buddhism of action. These are Christianity continued by other means, the same structure of valuation with the theological scaffolding quietly removed.
What I called the death of God in Zarathustra — in that work where Zarathustra enters the plague city, watches every form of pessimism parade past, and finally gives the explanation — is simultaneously the most terrible and the most hopeful event the prophet can name.6 Terrible because the ground is gone. Hopeful because the ground was a lie, and its removal is the condition of every genuine revaluation.
The morality that used God as its guarantor was, at its root, the idiosyncrasy of decadents: the fact "I am declining" transposed into the imperative "all of you ought to decline." When God dies, that imperative loses its cosmic endorsement.7 The question that follows is not whether to mourn. It is whether one has the strength to live without the shadow — to create values rather than inherit them, to become the lightning that the long storm of nihilism was preparing.
The end of Christianity—at the hands of its own morality (which cannot be replaced), which turns against the Christian God (the sense of truthfulness, developed highly by Christianity, is nauseated by the falseness and mendaciousness of all Christian interpretations of the world and of history; rebound from 'God is truth' to the fanatical faith 'All is false').The Will to Power, p. 7
'God is truth.' x 'God is love' 'the just God.' — The greatest event — 'God is dead' — only dully felt.Unpublished Fragments, pp. 376–378
Morality, henceforth without sanction, does not know how to maintain itself anymore. One finally lets the moral interpretation drop.Unpublished Fragments, pp. 376–378
Nihilism stands at the door: whence comes this uncanniest of all guests?... it is in one particular interpretation, the Christian-moral one, that nihilism is rooted.The Will to Power, p. 7
The entire European system of human striving feels itself partly 'meaningless,' partly 'immoral.' Probability of a new Buddhism. The highest danger.Unpublished Fragments, pp. 376–378
The plague city. He is warned, he is not afraid and goes inside, disguised. All kinds of pessimism parade by. The prophet interprets every parade... In the end Zarathustra gives the explanation: God is dead, this is the cause of the greatest danger? what? it could also be the cause of the greatest courage!Unpublished Fragments, pp. 374–376
The morality that would un-self man is the morality of decline par excellence—the fact, 'I am declining,' transposed into the imperative, 'all of you ought to decline'—and not only into the imperative.Ecce Homo, pp. 341–342