From POETRY by Bernard O'Donoghue

"Shelley's Romantic claim for the transcendent authority of poetry can be widely paralleled in other eras ever since the classical past. The most authoritative classical predecessor in raising the question is the Latin poet Horace who said that the function of poetry, broadly speaking, is to instruct, prodesse rather than delectare, to please. It is a choice which is certainly more significant than the matter of writing in verse forms or not, and one which has had a greater centrality in the discussion of poetry through history. Is the function of poetry primarily to instruct or to amuse? If it is a matter of instruction, this might warrant the grand authority Shelley ascribes to it. Sidney, without advancing the same claim for legislative authority, had declared that 'of all sciences…is our poet the monarch', intending 'the winning of the mind from wickedness to virtue'. So the obligation of public answerability in the poet may be seen as a subsection of poetry's general requirement of a sense of responsibility and moral worth."

Bernard O'Donoghue, Poetry: A Very Short Introduction, Oxford University Press, 2019, p. 7-8.