Knowledge is needed to acquire knowledge.
That is the core claim.
In order to have experience, and therefore in order to have the knowledge in which experience results, it is necessary that one’s mind be able to structure physical stimuli in a way that results in a coherent, ongoing stream of experience; and this, in its turn, presupposes the existence of innate cognitive structure.
Kant puts forth a number of arguments to validate this thesis of his, and these arguments are in most cases horribly defective, at least in their details. But the basic idea is cogent and important. And although it had been anticipated, notably by Plato and Leibniz, it had not been stated with the requisite degree of generality or force. In particular, it had not been pointed out that the very having of perceptions and of coherent perceptual experience requires the existence of cognitive machinery in which intelligence and knowledge are embedded.
Also, a few of Kant’s arguments are cogent in more or less the form in which he stated them, in particular, his argument to the effect that the relation of cause-effect, whose existence his predecessor David Hume denies, must in fact exist, since, without it, it would not be possible for there to exist being capable of denying its existence.
I go through the merits and demerits of Kant’s treatise in my book (now in audio book) Kant and Modern Philosophy.