We know that a judge and jury find a pre-mediatated crime to be far more serious than an accidental crime. The contemplation in preparation of a criminal act deepens its significance, and it becomes a part of a person's character.
Premeditated prayer works like that, only in a good way! Thinking about praying, planning for it, looking forward to it before the prayer occurs. The contemplation in preparation for prayer deepens the significance of our prayers and makes them part of our character.