God is the chief good, and supplies all need (Deu 10:9).
portion of mine inheritance and of my cup - may contain an allusion to the daily supply of food, and also to the inheritance of Levi (Deu 18:1, Deu 18:2).
maintainest - or, drawest out my lot - enlargest it. Psa 16:7 carries out this idea more fully.