Søren Aabye Kierkegaard on Faith and Reason

It is in the interest of faith to make a final, absolute decision. It is in the interest of the understanding to keep "deliberation" alive. Just as the police would be embarrassed if there were no crimes, so the understanding is embarrassed... if deliberation were completed. Faith wants the absolute; the understanding wants prolongation of thought.

There is only one proof--that of faith. It is impossible for a person to hold back his conviction and push ahead with reasons. If I actually have a firm conviction, then it is higher than reasons; it is actually the conviction that sustains the reasons, not the reasons which sustain the conviction. "Reasons" can lay an egg no more than a rooster can, at most a wind egg, and no matter how much intercourse they have with each other they never beget or bear a conviction. A conviction arises elsewhere.

There is only one proof for the truth of Christianity--the inward proof, argumentum spiritus sancti (the argument of the Holy Spirit). The Apostle John intimates this: "If we receive the testimony of men" (this is all the historical proofs and considerations), "the testimony of God is greater" --that is, the inward testimony is greater. And then, "He who believes the Son of God has the testimony in himself" (1 John 5:9,10).

It is not reasons that justify faith in God's son. Just the opposite--faith in God's Son is the testimony. Faith is the movement of infinity within itself, and it cannot be otherwise. Everything previous is preparatory, preliminary, something which disappears as soon as the conviction arrives. Otherwise there would be no resting in a conviction, for then to have conviction would mean to perpetually repeat the reasons. Faith itself is the testimony. Faith is the justification.