In what way does this fragment fit into the thematic concerns of the poet’s entire work?

In what way does this fragment fit into the thematic concerns of the poet’s entire work?

Know then thyself, presume not God to scan; The proper study of mankind is man. Plac'd on this isthmus of a middle state, A being darkly wise, and rudely great: With too much knowledge for the sceptic side, With too much weakness for the stoic's pride, He hangs between; in doubt to act, or rest; In doubt to deem himself a god, or beast; In doubt his mind or body to prefer; Born but to die, and reas'ning but to err; Alike in ignorance, his reason such, Whether he thinks too little, or too much: Chaos of thought and passion, all confus'd; Still by himself abus'd, or disabus'd; Created half to rise, and half to fall; Great lord of all things, yet a prey to all; Sole judge of truth, in endless error hurl'd: The glory, jest, and riddle of the world!