my heart. I myself, like "my soul". Figure of speech Synecdoche (of Part).
glory. Put by Figure of speech Metonymy (of Effect), App-6, for the powers of the mind which give the glory.
My flesh also shall rest. Refers to Messiah's death.
Related Commentaries of Psalms 16:9
Psalms 16:9
9 Therefore my heart is glad, and my glory rejoiceth: my flesh also shall restb in hope.