The Lord is my strength and song - He is the source of strength to me; and he is the subject of my praise. There is no ground of praise in myself for anything that I have done, but all is due to him.
And is become my salvation - He has saved me. I live because he preserved me. So we shall be saved in heaven solely because he saves us, and there, more than can be possible here, we shall say, "God is our strength and our song, and is become our salvation."

The LORD [is] my strength and (f) song, and is become my salvation.
(f) In that he was delivered, it came not from himself, not from the power of man, but only from God's favour, therefore he will praise him.

The Lord is my strength and song,.... It being in the name of the Lord the enemies of the psalmist were destroyed; and having obtained help of him when sore thrust at, he gives him all the glory, and ascribes nothing to himself. It was the Lord that strengthened him, helped him, and gave him the victory. The Lord is the author and giver of strength, natural and spiritual; he is the "strength" of the hearts and lives of his people, and of their salvation; and therefore is their "song", the matter of it: they sing of his nature and perfections, of his works of providence and grace, of his righteousness and salvation, as follows:
and is become my salvation; the author of temporal, spiritual, and eternal salvation; which the psalmist saw his interest in, and was assured of, and therefore sung praise on that account; see Exodus 15:2.

Salvation - My Saviour.