God told Abraham to kill his own son. Kierkegaard says that's what real faith demands.

By ordinary ethics, a father raising a knife over his son is a murderer, full stop. Kierkegaard's pseudonymous narrator argues Abraham was neither: faith required him to suspend the ethical entirely and obey a command that ethics itself condemns, trusting God beyond any reason he could explain to another person. That leap, not calm belief, is what Kierkegaard means by faith.

— Søren Kierkegaard (pseudonym: Johannes de Silentio), Fear and Trembling — 1843
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