The Lord [is] my strength
That is, the author both of natural and spiritual strength; that gave him strength of body, and fortitude of mind, to bear up under all the exercises he was tried with; the strength of his life, spiritual and temporal, and of his salvation; the strength of his heart under present distresses, and who he knew would be so in the hour of death, when his heart and strength would fail;
and my shield;
to protect and defend him; as were the love, power, and faithfulness of God, and the Lord Jesus Christ, his power and fulness, his blood, righteousness, and salvation;
my heart trusted in him;
in the Lord as his strength and shield; not in any creature, nor in his own strength and righteousness; but in the Lord God, in whom are righteousness and strength: and it is plain he did not trust in his own heart, since his heart trusted in the Lord; and which shows that his trust was an hearty one, his faith was a faith unfeigned, he believed with the heart unto righteousness;
and I am helped:
this was the fruit of his trust, even a gracious experience of divine assistance: saints are helpless in themselves, and are also as to the help of man; God is the only helper of them; he helps them out of all their troubles; in whatsoever he calls them unto, and to what they want; and the help he affords is sometimes quick, and always seasonable; and sometimes by means, and sometimes without them;
therefore my heart greatly rejoiceth;
that is, in the Lord, the ground of which was the help he had from him; and this joy was very great, a joy unspeakable, and full of glory; it was not carnal, but spiritual, a heart joy, joy in the Holy Ghost;
and with my song will I praise him;
praise is due to God, what glorifies him, and is acceptable to him; it becomes the saints, is comely for them, and it is pleasant work to them, when grace is in exercise; see ( Psalms 69:30 Psalms 69:31 ) ; this may be understood of one of his songs, and one of the best of them, and of one better than this, as a Jewish writer F21 observes.
F21 R. Moseh in Aben Ezra in loc.