9 But how shall we come there? “Happy is the man whose strength is in You”. He knew where he was, and that by reason of the frailty of his flesh he could not fly to that state of blessedness: he thought upon his own burden, as it is said elsewhere; “For the corruptible body weighs down the soul, and the earthly house depresses the understanding which has many thoughts.” The Spirit calls upward, the weight of the flesh calls back again downward: between the double effort to raise and to weigh down, a kind of struggle ensues: this struggle goes toward the pressure of the winepress.
Hear how the Apostle describes this same struggle of the winepress, for he was himself afflicted there, there he was pressed....“Miserable man that I am: who shall deliver me from the body of this death? The grace of God through Jesus Christ our Lord.”...“For I delight in the Law of God according to the inner man.” But what shall I do? How shall I fly? How shall I arrive there? “I see another law in my members,” etc....And as in the words of the Apostle, that difficulty and that almost inextricable struggle is alleviated by the addition, “The grace of God through Jesus Christ our Lord;” so here, when he sighed in the ardent longing for the house of God, and those praises of God, and when a kind of despair arose at the feeling of the burden of the body and the weight of the flesh, again he awoke to hope, and said, “Blessed is the man whose taking up is in You.”
Source: The Enarrations, or Expositions, on the Psalms (New Advent)