Removing obstacles to reconciliation with God by prayer, ritual or act. It involves remorse for sin (broken relationship with the divine), repentance (intent to change), and divine restoration of the relationship.
1. Atonement is a recurring theme in the history of primitive and established religions. It involves (a) concrete rites to remove sin, (b) cultic ceremonies to demonstrate remorse, (c) Mental expiation for individual purification, (d) humiliation before God, and (e) activities (good works) that demonstrate a changed life. Examples would be: Jewish Yom Kippur; Catholic Confession; Orthodox Jesus' Prayer; Brahmanic Prayascitta, and similarly purposed prayers and rites in Zoroastrianism, Islam, Buddhism, etc.
2. The Catholic Church has noted with joy that almost everywhere and at all times penitence has held a place of great importance, since it is closely linked with the intimate sense of religion which pervades the life of most ancient peoples as well as with the more advanced expressions of the great religions connected with the progress of culture.
In the Old Testament the religious sense of penitence is revealed with even greater richness. Even though man generally has recourse to it in the aftermath of sin to placate the wrath of God, or on the occasion of grave calamities, or when special dangers are imminent, or in any case to obtain benefits from the Lord, we can nevertheless establish that external penitential practices are accompanied by an inner attitude of "conversion," that is to say of condemnation of and detachment from sin and of striving toward God. One goes without food or gives away his property (fasting is generally accompanied not only by prayer but also by alms) even after sins have been forgiven and independently of a request for graces. One fasts or applies physical discipline to "chastise one's own soul," to "humble oneself in the sight of his own God," to "turn one's face toward Jehovah," to "dispose oneself to prayer," to "understand" more intimately the things which are divine or to prepare oneself for the encounter with God.
Penance therefore -- already in the Old Testament -- is a religious, personal act which has as its aim love and surrender to God: fasting for the sake of God, not for one's own self. Such it must remain also in the various penitential rites sanctioned by law. When this is not verified, the Lord is displeased with His people: "Today you have not fasted in a way which will make your office heard on high.... Rend your heart and not your garments, and return to the Lord your God." The social aspect of penitence is not lacking in the Old Testament. In fact, the penitential liturgies of the Old Covenant are not only a collective awareness of sin but constitute in reality a condition for belonging to the people of God.
We can further establish that penitence was represented even before Christ as a means and a sign of perfection and sanctity. Finally, we find among the just ones of the Old Testament those who offered themselves to satisfy with their own personal penitence for the sins of the community. All this, however, was but a foreshadowing of things to come. Penitence -- required by the inner life, confirmed by the religious experience of mankind and the object of a particular precept of divine revelation -- assumes "in Christ and the Church" new dimensions infinitely broader and more profound. The preeminently interior and religious character of penitence and the new wondrous aspects which it assumes "in Christ and in the Church" neither excludes nor lessens in any way the external practice of this virtue, but on the contrary reaffirms its necessity with particular urgency and prompts the Church -- always attentive to the signs of the times -- to seek, beyond fast and abstinence, new expressions more suitable for the realization, according to the character of various epochs, of the precise goal of penitence. Although penitence may be practised through abstinence from meat and fasting, other forms of penitence have been ratified to replace the observance of fast and abstinence with exercises of prayer and works of charity. (Papal Writings, Paenitemini, 1966).
In order for the act of atonement to influence social change, a social definition of the responsible "changed conduct" of the individual is required. In religious societies this strategy has often been used to bring conformity to diverse members of the society.
Atonement prayers and rites, both public and private, focus the attention of community members on the need for healthy relationships society with one another and with God.
Private atonement activities focus on the individual's relationship to God rather than on concrete social change.