Here "Jacob" represents the people of Israel. God being their "portion" is an idiom that means that they worship him. Alternate translation: "the portion of Israel" or "whom the people of Israel worship" (See: [[rc://en/ta/man/translate/figs-metonymy]] and [[rc://en/ta/man/translate/figs-idiom]])
This speaks of Israel belonging to Yahweh as if it were something that Yahweh gained through inheritance. Alternate translation: "The tribe of Israel belongs to him" (See: [[rc://en/ta/man/translate/figs-metaphor]])