This word does not occur in the Authorized Version of the New Testament except in Rom. 5:11, where in the Revised Version the word "reconciliation" is used. In the Old Testament it is of frequent occurrence.
The meaning of the word is simply at-one-ment, i.e., the state of being at one or being reconciled, so that atonement is reconciliation. Thus it is used to denote the effect which flows from the death of Christ.
But the word is also used to denote that by which this reconciliation is brought about, viz., the death of Christ itself; and when so used it means satisfaction, and in this sense to make an atonement for one is to make satisfaction for his offences (Ex. 32:30; Lev. 4:26; 5:16; Num. 6:11), and, as regards the person, to reconcile, to propitiate God in his behalf.
By the atonement of Christ we generally mean his work by which he expiated our sins. But in Scripture usage the word denotes the reconciliation itself, and not the means by which it is effected. When speaking of Christ's saving work, the word "satisfaction," the word used by the theologians of the Reformation, is to be preferred to the word "atonement." Christ's satisfaction is all he did in the room and in behalf of sinners to satisfy the demands of the law and justice of God. Christ's work consisted of suffering and obedience, and these were vicarious, i.e., were not merely for our benefit, but were in our stead, as the suffering and obedience of our vicar, or substitute. Our guilt is expiated by the punishment which our vicar bore, and thus God is rendered propitious, i.e., it is now consistent with his justice to manifest his love to transgressors. Expiation has been made for sin, i.e., it is covered. The means by which it is covered is vicarious satisfaction, and the result of its being covered is atonement or reconciliation. To make atonement is to do that by virtue of which alienation ceases and reconciliation is brought about. Christ's mediatorial work and sufferings are the ground or efficient cause of reconciliation with God. They rectify the disturbed relations between God and man, taking away the obstacles interposed by sin to their fellowship and concord. The reconciliation is mutual, i.e., it is not only that of sinners toward God, but also and pre-eminently that of God toward sinners, effected by the sin-offering he himself provided, so that consistently with the other attributes of his character his love might flow forth in all its fulness of blessing to men. The primary idea presented to us in different forms throughout the Scripture is that the death of Christ is a satisfaction of infinite worth rendered to the law and justice of God (q.v.), and accepted by him in room of the very penalty man had incurred. It must also be constantly kept in mind that the atonement is not the cause but the consequence of God's love to guilty men (John 3:16; Rom. 3:24, 25; Eph. 1:7; 1 John 1:9; 4:9). The atonement may also be regarded as necessary, not in an absolute but in a relative sense, i.e., if man is to be saved, there is no other way than this which God has devised and carried out (Ex. 34:7; Josh. 24:19; Ps. 5:4; 7:11; Nahum 1:2, 6; Rom. 3:5). This is God's plan, clearly revealed; and that is enough for us to know.