There are two kinds of knowledge: primary reflection and secondary reflection.
Primary reflection is essentially signal response. Animals are capable of this. Humans have this kind of knowledge as well.
Secondary reflection is knowledge performed by a self-conscious being that can say “I.” Self-consciousness allows for concept formation, which in turn makes language possible. This kind of knowledge is an immaterial act, since the reception of a concept is not reception of a material thing.
Secondary reflection yields two kinds of immaterial objects: non-material impersonal objects and non-material personal objects.
Non-material impersonal objects are things such as laws, mathematical formulas, and all universal concepts. These are not fully satisfactory to the human Self since they are impersonal and the Self is personal.
Non-material personal objects of knowledge are persons. These too are not fully satisfactory since they cannot answer every question that another person asks himself. But since this knowledge is of persons, it is more satisfactory than non-personal immaterial knowledge.
The difference between these two kinds of immaterial knowledge is that the first does not require belief. Impersonal objects reveal themselves consistently since they have no freedom. But personal objects, having freedom, must be trusted in order to be known. Hence, knowledge of persons requires belief/faith in the other.
Knowledge/belief in persons is the highest kind of knowledge since it is non-material and personal.
Yet it only begins when one loves another. Only love opens one to the revelation of the other as person. Without love, the other is only immaterial impersonal object, not immaterial personal object. Love alone reveals the other as ultimately unknowable on a complete level without trust and commitment. Love reveals and understands the personhood of the other.
Therefore, love, since it alone is adequate to the highest form of knowledge – knowledge of immaterial personal objects – is itself the highest form of knowledge.