The Savior Himself is He Whom we are asked to put on. It is one and the same thing to say, 'Put on the whole armor of God,' and 'Put on the Lord Jesus Christ.' Our belt is truth and our breastplate is righteousness. The Savior is also called both 'truth' and 'righteousness.' On this principle He is also to be understood as the 'Gospel of peace.' He is Himself the 'shield of faith' and the helmet of salvation. He is the 'sword of the Spirit,' because He is the Word of God, living and efficacious, the utterance of which is stronger than any helmet and sharp on both sides.
-St. Jerome, Unknown, 5th century


The mind of a heedful man is as it were a watchman on duty, or an unsleeping guard of the inner Jerusalem. Standing at the height of spiritual contemplation, he looks with an eye of purity upon the enemy powers who go around and attack his soul, in accordance with the Psalmist: 'And my eye hath looked down upon my enemies' (Ps. 53:9). From his eye the devil is not hidden, who 'as a roaring lion walketh about seeking whom he may devour' (I Pet. 5:8), nor are they who bend their bow 'to shoot in the dark the upright of heart (Ps. 10:2). And thus such a man, following the teaching of the divine Paul, receives 'the whole armor of God, that [he] may be able to withstand in the evil day (Eph. 6:13), and with this armor and with the cooperating grace of God, he repels visible attacks and vanquishes invisible warriors.
-St. Seraphim of Sarov, Spiritual Instructions no. 30, Little Russian Philokalia Vol. 1; Saint Herman of Alaska Brotherhood pgs. 48-49, 19th century