“The psalmist uses the word ‘prevail’ (Ps. 117:2); that is, God’s grace ‘rules’ over us. It is a kingdom of grace that is more powerful in and over us than all anger, sin, and evil. ‘Prevail,’ גָּבַר in Hebrew, means to be supreme, to be great.
You must think of the kingdom of grace as a child might, in this way: God, through the Gospel, has set a new and great heaven over us who believe, and this is called the heaven of grace. It is far, far more immense and beautiful than this visible heaven; and it is eternal, certain, and indestructible as well.
Although sin makes itself felt, death bares its teeth, and the devil frightens us, still there is far more grace to prevail over all sin, far more life to prevail over death, and far more God to prevail over all devils.
In this kingdom sin, death, and the devil are nothing more than the black clouds of the material heaven. For a time they may well conceal heaven, but they cannot prevail. They must stay beneath the heavens and suffer it to remain, prevail, and rule over them; and at last they must pass away.
Therefore although sin bites us, death frightens us, and the devil throws his weight around with temptation, these are still only clouds. The heaven of grace prevails and rules; in the end they must remain below and surrender.
This cannot come through works, but only through the faith which is certain that such a heaven of grace is above it, without works, and which looks to this heaven as often as it sins or feels sin, comforting itself without merit or works.”
–Martin Luther, Luther’s Works, Vol. 14: Selected Psalms III (ed. Jaroslav Jan Pelikan, Hilton C. Oswald, and Helmut T. Lehmann; vol. 14; Saint Louis: Concordia Publishing House, 1999), 14: 27. Luther is commenting on Psalm 117.