Here in a nutshell Dietrich Bonhoeffer explains why the Christian community gives itself to the reading of the Scriptures as a living whole.
It is not in our life that God's help and presence must still be proved, but rather God's presence and help have been demonstrated for us in the life of Jesus Christ. It is in fact more important for us to know what God did to Israel, to His Son Jesus Christ, than to seek what God intends for us today. The fact that Jesus Christ died is more important than the fact that I shall die, and the fact that Jesus Christ rose from the dead is the sole ground of my hope that I, too, shall be raised on the Last Day. Our salvation is "external to ourselves." I find no salvation in my life history, but only in the history of Jesus Christ. Only he who allows himself to be found in Jesus Christ, in his incarnation, his Cross, and his resurrection, is with God and God with him.
The Bible is many things, but first and foremost it's the record of God's mighty work of salvation culminating in Christ. In Bonhoeffer's words it is "the holy history of God on earth." It's there we learn to believe that the God of Abraham, Isaac and Jacob is our God too, and that the Father of Jesus Christ is also our Father.
Quote from Life Together, p. 54