Jesus we know, the son of God, God we know, and the holy spirit we know, the third person of the trinity but I must confess there's not much more that I know. I know yes the Holy Spirit helps us understand the things of God but as the book points out, there's knowing and there's knowing about. Most of what we know is this 'know about' knowledge, knowledge we gain through the study of the word, through accounts from other people but there's a deeper, more personal 'knowing' that comes through experience and revelation from God through the spirit of God. This knowledge is far greater than any of our human efforts, all our intellectual capability. I don't know about you but I'm not a very smart person so this kind of knowledge is appealing to me. Let me repost something from the book by some guy, Athanasius who wrote something he called 'The Incarnation of the Word of God'. Here we go.
But for the searching of the Scriptures and true knowledge of them, an honorable life is needed, and a pure soul, and that virtue which is according to Christ; so that the intellect guiding its path by it may be able to attain what it desires, and to comprehend it, in so far as it is accessible to human nature to learn concerning the Word of God. For without a pure mind and a modeling of the life after the saints, a man could not possibly comprehend the mind of the saints....He that would comprehend the mind of those who speak of God needs begin by washing and cleansing his soul.
-ONWARD