According to Sidney, if we don't experience pleasure in the process of learning, we won't have the incentive to learn. This is where poetry comes in: it is imaginative and creative and therefore offers pleasure in the way other types of learning might not. It can, therefore, draw people toward knowledge and learning that they would otherwise try to avoid.
Sidney speaks of this in the context of "Indians," or Native Americans, who he says don't have "learning" (at least as Europeans understood it in an academic context) in their cultures. He says that the only way learning can come to them is if they have their "hard wits softened" by the "delights of poetry." As he puts it,
until they find a pleasure in the exercise of the mind, great promises of much knowledge will little persuade them that know not the fruits of knowledge.
Sidney also mentions the Welsh, who were subject to frequent invasions, with invading forces sometimes trying to eradicate all learning among them. Sidney says that despite the attempts to do so, the Welsh maintained learning through poetry, noting "their poets even to this day last." This is because poetry has been a source of pleasure to them.
Sidney recognizes that dull drudgery alone does not inspire must interest in learning, even if the information is useful and there is a practical incentive to pursue it. Pleasure, in contrast, provides positive motivation, and the beautiful worlds a poet creates can thus become portals into knowledge and information.