The Bible's central message is the story of salvation, and throughout both testaments three strands in this unfolding story can be distinguished: the bringer of salvation, the way of salvation and the heirs of salvation. This could be reworded in terms of the covenant idea by saying the central message of the Bible is God's covenant with men, and that the strands are the mediator of the covenant, the basis of the covenant, and the covenant people. God himself is the Saviour of His people; it is He who confirms His covenant mercy with them. The bringer of Salvation, the mediator of the covenant is Jesus Christ, the Son of God. The way of salvation, the basis of the covenant, is God's grace, calling forth from his people a response of faith and obedience. The heirs of salvation, the covenant people are the Israel of God, the Church of God.
F.F. Bruce, New Bible Dictionary, Second edition, p. 139.