The Lord is my strength - See the notes at Psalms 18:1.
And my shield - See the notes at Psalms 3:3. Compare Psalms 33:20; Psalms 59:11; Psalms 84:9; Psalms 89:18; Genesis 15:1.
My heart trusted in him - I trusted or confided in him. See Psalms 13:5.
And I am helped - I have found the assistance which I desired.
Therefore my heart greatly rejoiceth - I greatly rejoice. I am happy. He had found the assurance of the divine favor which he desired, and his heart was glad.
And with my song will I praise him - I will sing praises to Him. Compare Psalms 22:25.