The name of the Saviour God was invoked only once in the year by the high priest in atonement for the sins of Israel, after he had sprinkled the mercy seat in the Holy of Holies with the sacrificial blood. The mercy seat was the place of God's presence. When St. Paul speaks of Jesus whom "God put forward as an expiation by his blood", he means that in Christ's humanity "God was in Christ reconciling the world to himself."
Source: Catechism of the Catholic Church (Vatican.va)