Sydney wrote this essay in part to counter claims by some that poetry and such imaginative work had become a tool for corruption. In response, Sydney tries to claim that poetry is in fact one of the highest art forms, and to support his argument he presents poetry as being something that has been present in all cultures and as being essential to mankind's expression of itself. Note what Sydney argues about poetry:

And first, truly, to all them that, professing learning, inveigh against poetry, may justly be objected that they go near to ungratefulness, to seek to deface that which, in the noblest nations and languages that are known, hath been the first light-giver to ignorance, and first nurse, whose milk little by little enabled them to feed afterwards of tougher knowledges.

Poetry, Sydney argues, is something that is superior to both philosophy and history when it comes to teaching humans about morality, and he uses a number of examples to support his claim. Poetry is presented in this essay as being the most important method that allows humans to learn virtue, and his comparison to breast feeding strengthens this impression of poetry as being a moral force for good and virtue. It therefore appears that it is the claims of those who argued that poetry necessarily led to corruption and vice that are vague and elusive. Sydney goes some way to present at least a cogent defence of his opinions and views.