The LORD is my strength and my song; he has become my salvation.
PSALM 118 At the time when this psalm was penned, whenever that was, David having attained to the possession of royal power, and aware that he reigned for the common safety of the Church, calls upon all the children of Abraham to ponder attentively this grace. He also recounts his dangers, the magnitude and variety of which would have slain him a hundred times, had not God wonderfully succored him.
Commenting on Psalm 118:1-29
The Lord my strength and song, my strength while I was in the conflict, my song now that it is ended; my strength against the strong, and my song over their defeat. He is far from boasting of his own valour; he ascribes his victory to its real source, he has no song concerning his own exploits, but all his peans are unto Jehovah Victor...
It appears here, as often as elsewhere, that David had his heart full of the goodness of God. He loved to think of it, loved to speak of it, and was very solicitous that God might have the praise of it and others the comfort of it. The more our hearts are impressed with a sense of God's goodness the more they will be enlarged in all manner of obedience.
Commenting on Psalm 118:1-18