9 “Mine is Galaad”. These names are read in the Scriptures of God. Galaad has the voice of an interpretation of its own and of a great Mystery: for it is interpreted “the heap of testimony.” How great a heap of testimony in the Martyrs? “Mine is Galaad,” mine is a heap of testimony, mine are the true Martyrs....Then meanly esteemed was the Church among men, then reproach on Her a Widow was being thrown, because Christ's She was, because the sign of the Cross on her brow She was wearing: not yet was there honour, censure there was then: when therefore not honour, but censure there was, then was made a heap of witness; and through the heap of witness was the Love of Christ enlarged; and through the enlargement of the Love of Christ, were the Gentiles possessed.
There follows, “And mine is Manasses;” which is interpreted forgotten. For to Her had been said, “Confusion for everlasting You shall forget, and of the reproach of Your widowhood You shall not be mindful.” There was therefore a confusion of the Church once, which now has been forgotten: for of Her confusion and of the “reproach” of Her widowhood now She is not mindful. For when there was a sort of confusion among men, a heap of witness was made. Now no longer does any even remember that confusion, when it was a reproach to be a Christian, now no one remembers, now all have forgotten, now “Mine is Manasses, and Ephraim the strength of My head.”
Ephraim is interpreted fruitfulness. Mine, he says, is fruitfulness, and this fruitfulness is the strength of My Head. For My Head is Christ. And whence is fruitfulness the strength of Him? Because unless a grain were to fall into the earth, it would not be multiplied, alone it would remain. Fall then to earth did Christ in His Passion, and there followed fruit-bearing in the Resurrection. He was hanging and was being despised: the grain was within, it had powers to draw after it all things.
How in a grain do numbers of seeds lie hidden, something abject it appears to the eyes, but a power turning into itself matter and bringing forth fruit is hidden; so in Christ's Cross virtue was hidden, there appeared weakness. O mighty grain! Doubtless weak is He that hangs, Doubtless before Him that people did wag the head, Doubtless they said, “If Son of God He is, let Him come down from the Cross.” Hear the strength of Him: that which is a weak thing of God, is stronger than men. With reason so great fruitfulness has followed: it is mine, says the Church.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)