My flesh - faileth - I shall soon die: and my heart - even my natural courage, will fail; and no support but what is supernatural will then be available. Therefore, he adds:
God is the strength of my heart - Literally, the rock of my heart.
And my portion - Allusion is here made to the division of the promised land. I ask no inheritance below; I look for one above. I do not look for this in the possession of any place; it is God alone that can content the desires and wishes of an immortal spirit. And even this would not satisfy, had I not the prospect of its being for ever, לעולם leolum , "to eternity!'