He must therefore really live in the godless world, without attempting to gloss over or explain its ungodliness in some religious way or other. He must live a ‘secular’ life, and thereby share in God’s sufferings. He may live a ‘secular’ life (as one who has been freed from false religious obligations and inhibitions). To be a Christian does not mean to be religious in a particular way, to make something of oneself (a sinner, a penitent, or a saint) on the basis of some method or other, but to be a man – not a type of man, but the man that Christ creates in us.
It is not the religious act that makes the Christian, but participation in the sufferings of God in the secular life. That is metanoia: not in the first place thinking about one’s own needs, problems, sins, and fears, but allowing oneself to be caught up into the way of Jesus Christ, into the messianic event, thus fulfilling Isa. 53. Therefore ‘believe in the gospel’, or, in the words of John the Baptist, ‘Behold, the Lamb of God, who takes away the sin of the world’ (John 1.29).
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Source: Dietrich Bonhoeffer, Letters and Papers from Prison
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