I have begun my second reading of Desiring God. This time I am reading a chapter a week and then discussing it with a friend. I find that discussion and study are much more helpful in retaining information, rather than simply reading through a book and moving on to the next one.
John Piper rights on page 44 that,
In creation, God “went public” with the glory that reverberates joyfully between Father and the Son. There is something about the fullness of God’s joy that inclines it to overflow.
Why did God create the world and humanity? To share with others His joy in Himself.