The book of Psalms has attracted more attention from Christians than any other Old Testament book. Its popularity dates back to the New Testament itself, where one finds frequent quotes and allusions to it. Christians today consider it the heart of the Old Testament. It is intellectually and emotionally stimulating. The piety and devotional mood that permeate the psalms and that find their origin in an intense personal relationship with God strikes a responsive chord among modern men and women. Certain phrases of the Psalter (e.g., “the LORD is my shepherd” [Ps. 23:1]) are familiar and reassuring. One feels at home in the Psalter.
When examined closely, however, the Psalter surprises us and we have difficulty understanding its message. For one thing, the individual psalms seem to be without a context, either historical or literary, in a way that is virtually unique to the Old Testament. In the second place, the attitude of the psalmist is occasionally hard to comprehend for a Christian who has been taught to recognize his own sin and also to love his enemies. - Raymond B. Dillard and Tremper Longman III - An Introduction to the Old Testament