12 “He makes wars to cease unto the end of the earth”. This not yet see we fulfilled: yet are there wars, wars among nations for sovereignty; among sects, among Jews, Pagans, Christians, heretics, are wars, frequent wars, some for the truth, some for falsehood contending. Not yet then is this fulfilled, “He makes wars to cease unto the end of the earth;” but haply it shall be fulfilled. Or is it now also fulfilled? In some it is fulfilled; in the wheat it is fulfilled, in the tares it is not yet fulfilled.
What is this then, “He makes wars to cease unto the end of the earth”? Wars He calls whereby it is warred against God. But who wars against God? Ungodliness. And what to God can ungodliness do? Nothing. What does an earthen vessel dashed against the rock, however vehemently dashed? With so much greater harm to itself it comes, with how much the greater force it comes. These wars were great, frequent were they. Against God fought ungodliness, and earthen vessels were dashed in pieces, even men by presuming on themselves, by too much prevailing by their own strength.
This is that, the shield whereof Job also named concerning one ungodly. “He runs against God, upon the stiff neck of his shield.” What is, “upon the stiff neck of his shield”? Presuming too much upon his own protection. Were they such who said, “God is our refuge and strength, a Helper in tribulations which have found us out too much”? Or in another Psalm, “For I will not trust in my bow, neither shall my sword save me.” When one learns that in himself he is nothing, and help in himself has none, arms in him are broken in pieces, wars are made to cease.
Such wars then destroyed that Voice of the Most High out of His holy clouds, whereby the earth was moved, and the kingdoms were bowed. These wars has He made to cease unto the end of the earth. “He shall break the bow, and dash in pieces the arms, and burn the shield with fire.” Bow, arms, shield, fire. The bow is plots; arms, public warfare; shields, vain presuming of self-protection: the fire wherewith they are burned, is that whereof the Lord said, “I have come to send fire on the earth;” of which fire says the Psalm, “There is nothing hid from the heat thereof.” This fire burning, no arms of ungodliness shall remain in us, needs must all be broken, dashed in pieces, burned.
Remain thou unharmed, not having any help of your own; and the more weak you are, having no arms your own, the more He takes you up, of whom it is said, “The God of Jacob is our taker up.”...But when God takes us up, does He send us away unarmed? He arms us, but with other arms, arms Evangelical, arms of truth, continence, salvation, faith, hope, charity. These arms shall we have, but not of ourselves: but the arms which of ourselves we had, are burnt up: yet if by that fire of the Holy Spirit we are kindled, whereof it is said, “He shall burn the shields with fire;” you, who wished to be powerful in yourself, has God made weak, that He may make you strong in Him, because in yourself you were made weak.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)