I don't really know John Piper, and he certainly doesn't know me, but nonetheless I consider him a dear friend. I love him because, through his books, sermons, and life, God has more fully revealed Himself to me and given me more joy in Him. That is a priceless service.
I paid a visit to an old friend this morning - here's a few nuggets from the beginning of the 2003 edition of Desiring God.
"God threatens terrible things if we will not be happy" - Jeremy Taylor
"The joy of the Lord is your strength." - Nehemiah (8.10)
"May the Living God, who is the portion and rest of the saints, make our carnal minds so spiritual, and our earthly hearts so heavenly, that loving him, and delighting in him, may be the work of our lives." - Richard Baxter
"The joy of the Lord will arm us against the assaults of our spiritual enemies and put our mouths out of taste for those pleasures with which the tempter baits his hooks." - Matthew Henry
"It is unbiblical and arrogant to try to worship God for any other reason than the pleasure to be had in Him." - John Piper
"There once was in man a true happiness of which now remain to him only the mark and empty trace, which he in vain tries to fill from all his surroundings, seeking from things absent the help he does not obtain in things present. But these are all inadequate, because the infinite abyss can only be filled by an infinite and immutable object, that is to say, only by God Himself." - Blaise Pascal
"God is not worshiped where He is not treasured and enjoyed. Praise is not an alternative to joy, but the expression of joy. Not to enjoy God is to dishonor Him." - John Piper
"I find in the Bible a divine command to be a pleasure-seeker - that is, to forsake the two-bit, low-yield, short-term, never-satisfying, person-destroying, God-belittling pleasures of the world and to sell everything 'with joy' (Mt. 13.44) in order to have the kingdom of heaven and the 'enter in to the joy of your master' (Mt. 25.21, 23)." - John Piper