This work was written around 1579 (although not published until 1595, after the author's death) as a response to attacks on imaginative literature in an era of Puritan influence. According to Puritanical thought, art was at best irresponsible and at worst morally corrupting. Poetry was becoming particularly singled out for criticism - for example in Stephen Gosson's The Schoole of Abuse. In the Defence of Poesie, Sidney replied that poetry could be used for moral purposes, that it was not vulgar entertainment but a beautiful and noble art which could improve its readers. With this work, Sidney helped stem the tide of criticism against poetry in his own time and his arguments remained influential in helping to exalt poetry to a high status, especially in the era of high Romanticism in the nineteenth century.
Sidney's "Defense of Poesie" was written at a time when poetry as a literary form faced criticism from two sides. On the one hand, many religious figures believed that poetry was inherently depraved, a literary form that celebrated the trite and frivolous at best, the pornographic and obscene at worst. One of these writers, a Puritan named Stephen Gosson, compared poetry to cooking, emphasizing its earthy appeal:
The pleasures of the one winnes the body from labor, and conquereth the sense; the allurement of the other drawes the mind from vertue, and confoundeth wit.
On the other, many literary critics (many of whom were themselves religious figures) argued that poetry required little real talent, and that it should not be taken seriously. Against these two lines of thinking, Sidney argued that poetry always had been a force for moral uplift. Agreeing with those who condemned scurrilous poetry, he urged English poets to take on important themes, especially in epic poetry. He thought that poetry itself was not inherently bad, but that the form had been corrupted by lesser poets. Appealing to a sense of nationalism that was beginning to hold sway in sixteenth-century England, he emphasized the importance of poetry in establishing vernacular languages in France and Italy. In short, he claimed that poetry had a unique ability to elevate the human soul. The historical significance of this essay is that it represented a salvo in what might be called a "culture war" in England. Calvinists were waging a pointed critique against what they saw as corruption and impiety, humanists were producing works that celebrated the human condition, and, as mentioned earlier, the concept of a modern English nation-state and national identity was beginning to emerge. It was in this milieu that some of the greatest works in English literature—Shakespeare and Spenser, for example—emerged.