Commentary for Psalms 16:9

Therefore, my heart rejoiced, etc. because I am confident that You will not forsake my soul to the grave. Since, concerning the iniquity of a grave transgression which I committed, You sent me the tidings (in II Sam. 12:13): “Also the Lord has removed your sin,” certainly from now on You will not forsake me [to cause me] to turn away from You.

Therefore my heart is glad: – Because I have put Thee before me always my heart is glad.

and my glory exulteth: – that is, the soul, which is the glory of the body; for I am confident that when it is separated from the body it will cleave to its Creator.