"I have no knowledge of myself as I am but only as I appear to myself. The consciousness of oneself is therefore very far from being a knowledge of oneself."? What does Immanuel Kant means in this quote?

The inability to have objective knowledge because that would mean “knowing the thing in itself”, which is according to Kant, unknowable. A pertinent question to ask is why must there be a division between perception and an unknowable “thing in itself”? Is it to protect science as a methodology that requires ongoing skepticism in the form of a deflection against ever arriving at “final truths”? Or, is it rather, as Nietzsche suspected, a means Kant came up with to protect the inviolable nature of some sort of concept of “God”?