Intercession is service - the chief service of a life on God's plan. It is unlike all other forms of service, and superior to them in this: it has fewer limitations. In all other service we are constantly limited by space, bodily strength, equipment, material obstacles, and difficulties arising from differences of personality.
Prayer knows no such limitations. It ignores space. It may be free from the expenditure of bodily strength when rightly practiced and one's powers are under proper control. It goes directly, by the communication of spirit, into men's hearts, quietly passes through walls and past locks unhindered, and comes into direct touch with the inner heart and will.
In service, as ordinarily understood, one is limited to the space where his body is, the distance his voice can reach, and the length of time he can keep going before he must stop to eat, rest, or sleep. He is limited by walls and locks, by the prejudices of men's minds, and by differences of temperament that must be considered in seeking to reach men's hearts. None of these physical obstacles hinder true, Spirit-led prayer.
The strategy that wins spiritual battles puts intense, prayer-closet fighting first - before all else.