Eventually, we reach human beings, and we find that we have two more additional immanent activities: mind/intellect and will.
Here, cognition is awareness of the object, unqualified. Our understanding of objects is not limited to just the signs of sensation themselves, rather, we can know the reality, the being, behind the signs.
Intellect can thusly know the interiority of things, like its immanent activities, their aims and ends, interior principles from which they arise, etc., including our own. Intellect can even know itself, it can even know its own activities, its own thoughts, and by reflecting on them, comparing them to the objects in the world, can experience thoughts and knowledge as true or false.
Not only that, but intellect can also make our thoughts about the simularities between things themselves objects of thoughts, which is what we mean when we say that the intellect can understand universals.
When the experience of true and false is coupled with the universality of intellect, they form the basis of systems of science, mathematics, philosophy, religion, etc.
Will, on the other hand, arises from this awareness of the object-in-itself. Will doesn’t just love an object because of how useful it is, but loves it for its own sake. This is why only humans make art, only we want to create an object that exists for its own sake, with a history, aesthetic, narrative…with a kind of personality.
And when that object is a person, will can love a person for his own sake.
And of course, the will also references what is good for the person.
Because of the universality of the intellect, the will desires abstract objects like moral principles and the like, things that can have a variety of particular applications. This is the basis for our free choice, that we can choose between the particular applications of these abstract principles (although a lot of our choice is determined by circumstances and our own character as well).
Anyway, what Mr. Sheed has in mind when he speaks of knowledge and love is the latter sort, which is “spiritual” in the sense that it operates without the need of a bodily organ, and in the sense that it allows for knowledge of God.
I’d be happy to try and answer any questions you might have