R.C. Sproul, The Purpose of God, An Exposition of Ephesians, Christian Focus Publications, 1994, p. 152.
All of our warfare and all of our activity must take place in the context of constant, unceasing prayer. Just as a soldier on the battle line has to keep in constant communication with his general headquarters and his commanding officer, so the Christian who is on the battle line must be in constant communication with his Lord. He might be fully equipped with all the armor, but if he is cut off from personal communication with his own commander, then he will be isolated and vulnerable.
R.C. Sproul, The Purpose of God, An Exposition of Ephesians, Christian Focus Publications, 1994, p. 152.