Commentaries:
Barnes' Notes
The Lord is the portion of mine inheritance - In contradistinction from idols. The margin here is, "of my part." The word properly means "lot, portion, part;" and is applicable to the portion of booty or plunder that fell to anyone; or to the portion of land that belonged to anyone in the division of an estate, II Kings 9:10, II Kings 9:36-37. The meaning here is, that Yahweh was the being whom the psalmist worshipped as God, and that he sought no possession or comfort which did not proceed from him.
And my cup - The allusion here is to what we drink; and hence, the term is used in the sense of "lot" or "portion." See the notes at Isaiah 51:17. Compare the notes at Psalms 11:6. The idea here is this: "The cup that I drink - that cheers, refreshes, and sustains me - is the Lord. I find comfort, refreshment, happiness, in him alone; not in the intoxicating bowl; not in sensual joys; but in God - in his being, perfections, friendship."
Thou maintainest my lot - Thou dost defend my portion, or that which is allotted to me. The reference is to what he specifies in the following verse as his inheritance, and he says that that which was so valuable to him was sustained or preserved by God. He was the portion of his soul; he was the source of all his joy; he maintained or preserved all that was dear to his heart.
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