To understand who Jesus is as the one who saves (his doing) because he is Savior (his being), it's vital to see the doctrine of salvation in the context of the doctrines of the Trinity and the Incarnation. These doctrines tell us that the triune God of love (Trinity), in the person of the Son of God, became human (Incarnation).
As we celebrate Christmas, let us remember that the Incarnation was not merely something that God did, but as what God became. The Incarnation is fundamental to the very being of God. God did not "put on" humanity, he became human--he added humanity to his divinity and so became Savior. And the salvation that is ours, is who Jesus actually is. He is "both consubstantial with the Father according to the Godhead, and consubstantial with us according to the Manhood." Jesus is not merely "like" God, he is God. And Jesus is not "like" a human person, he is one. "'The incarnation,' Torrance stresses, 'is to be understood as God really become man'" (loc 1271). Torrance elaborates:
The incarnation was not the bringing into being of a created intermediary between God and man, but the incarnating of God in such a way that in Jesus Christ he is both God and man in the fullest and most proper sense. The incarnation is to be understood then, as a real becoming on the part of God, in which God comes as man and acts as man, all for our sake--from beginning to end God the Son acts among us in a human way, "within the measures of our humanity" (loc 1271).Eugenio comments:
The affirmation that Jesus Christ is not just God in humanity, but God as human, implies a rejection of the idea that the humanity of Christ was merely instrumental in the hands of God.While maintaining this, Torrance also emphasizes the originality and newness of the incarnation: "In the incarnation of the Son something new has taken place in God. This, however, does not only refer to the virgin birth, or to the fact that God became human. Rather, the whole life of the incarnate Son is new to God, including being in creaturely space and time, experiencing human emotions and needs... The rationale Torrance provides for his new becoming in the life of the eternal God has to do with his theology of vicarious redemption. Quoting Athanasius, "He was not man previously, but he became man for our sake." And precisely because God himself became human, he himself is the agent of reconciliation (loc 1285).Eugenio adds this important insight: "In so far as redemption requires both God's initiative and humanity's response, both are seen to have been accomplished by the one God-man, Jesus Christ" (loc 1298). And so, again, Torrance has emphasized for us that salvation is not merely what God does, but what God, himself, is in the person of the one God-man, the incarnate Son of God, Jesus Christ. As the Christmas hymn urges us: "O, come let us adore him!"