From Bonhoeffer’s Life Together:

Almost all of us have grown up with the idea that the Scripture reading is only a matter of hearing the Word of God for this particular day. That is why for many the Scripture reading consists of only a few, brief, selected verses which are to form the guiding thought of the day . . . But there can be equally little doubt that brief verses cannot and should not take the place of reading the Scripture as a whole. The verse for the day is still not the Holy Scripture which will remain throughout all time until the Last Day. Holy Scripture is more than a watchword. It is also more than “light for today.” It is God’s revealed Word for all men, for all times. Holy Scripture does not consist of individual passages; it is a unit and is intended to be used as such.

As a whole the Scriptures are God’s revealing Word. Only in the infiniteness of its inner relationships, in the connections of Old and New Testaments, of promise and fulfillment, sacrifice and law, law and gospel, cross and resurrection, faith and obedience, having and hoping, will the full witness of Jesus Christ the Lord are perceived. This is why common devotions will include, besides the prayer of the psalms, a longer reading from the Old and the New Testament.