What are the various ways that Buber uses the language of “spirit” to speak about human nature and human relation to spiritual beings?

How does Buber employ the concept of human love in his explanation of how human beings enter into relation with one another in the world of Thou? Why is human love significant?

Does Buber think that the explicit concept of God is necessary, or is the existence of the Eternal Thou enough? Do you agree with his position? Why or why not?