In theology, a sin is described as mysterium iniquitatis and absolution from it— mysterium salutis or pietatis. In the New Testament a sin is always connected with absolution, “forgiveness,” and sinners are of great concern for Jesus. Nevertheless, modern culture becomes more and more detached from Christian tradition and thus deprives a human being of the spiritual values and makes him become further impoverished. This article provides a synthetic discussion of the reality of a sin—“mystery of illicitness” and also reflects on repentance and reconciliation with God and with one’s own neighbour. The reflections presented in this article are based on the teachings of the contemporary Church and on the Papal teachings especially.