2 Say we, therefore, ourselves also: “Hearken, O God, to my prayer, while I am troubled; from fear of the enemy deliver my soul”. Enemies have raged against the Martyrs: for what was that voice of Christ's Body praying? For this it was praying, to be delivered from enemies, and that enemies might not have power to slay them. Were they not therefore hearkened to, because they were slain; and has God forsaken His servants of a contrite heart, and despised men hoping in Him?
Far be it. For “who has called upon God, and has been forsaken; who has hoped in Him, and has been deserted by Him?” They were hearkened to therefore, and they were slain; and yet from enemies they were delivered. Others being afraid gave consent, and lived, and yet the same by enemies were swallowed up. The slain were delivered, the living were swallowed up. Thence is also that voice of thanksgiving, “Perchance alive they would have swallowed us up.”...Therefore for this prays the voice of the Martyrs, “From fear of the enemy deliver my soul:” not so that the enemy may not slay me, but that I may not fear an enemy slaying.
For that to be fulfilled in the Psalm the servant prays, which but now in the Gospel the Lord was commanding. What but now was the Lord commanding? “Fear not them that kill the body, but the soul are not able to kill; but Him rather fear ye, that has power to kill both body and soul in the hell of fire.” And He repeated, “Yea, I say unto you, fear Him.” Who are they that kill the body? Enemies. What was the Lord commanding? That they should not be feared. Be prayer offered, therefore, that He may grant what He has commanded.
“From fear of the enemy deliver my soul.” Deliver me from fear of the enemy, and make me submit to the fear of You. I would not fear him that kills the body, but I would fear Him that has power to kill both body and soul in the hell of fire. For not from fear would I be free: but from fear of the enemy being free, under fear of the Lord a servant.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)