Dietrich Bonhoeffer (emphasis mine):

Only another Christian who is under the cross can hear my confession. It is not experience with life but experience of the cross that makes one suited to hear confession. The most experienced judge of character knows infinitely less of the human heart than the simplest Christian who lives beneath the cross of Jesus. The greatest psychological insight, ability and experience cannot comprehend this one thing: what sin is. Psychological wisdom knows what need and weakness and failure are, but it does not know the ungodliness of the human being. And so it also does not know that human beings are ruined only by their sin and are healed only by forgiveness. The Christian alone knows this. In the presence of a psychologist I can only be sick; in the presence of another Christian I can be a sinner. The psychologist must first search my heart, and yet can never probe its innermost recesses. Another Christian recognizes just this: here comes a sinner like myself, a godless person who wants to confess and longs for God’s forgiveness. The psychologist views me as if there were no God. Another believer views me as I am before the judging and merciful God in the cross of Jesus Christ. When we are so pitiful and incapable of hearing the confession of one another, it is not due to a lack of psychological knowledge, but a lack of love for the crucified Jesus Christ.

HT: Tim Chester