Note 1406 — AN ESSAY ON MAN, IN FOUR EPISTLES (continued 3)
Reading edition
Pope personified happiness at the beginning, but seems to have dropped that idea in the seventh line, where the deity is suddenly transformed into a plant, from whence this metaphor of a vegetable is carried on through the eleven succeeding lines till he suddenly returns to consider happiness again as a person, in the eighteenth line.—Warton.
The change from a person to a thing commences at the third verse, where Pope calls happiness "that something," and he changes back to the person in the eighth verse, where he addresses happiness as "thou."