This set of posts comes from Pastor Mark Driscoll and his wife Grace. The sermon series The Peasant Princess brought up dozens of questions that they felt they should respond to. The result is this blog series: Christian Sex: Frank Answers to Honest Questions.
Answer: Many Christian pastors have tried in vain to find mention of masturbation in Scripture so they can condemn and forbid it. Unable to find any verses on the matter, some have foolishly used the story of Onan in Genesis 38:6-10 as their proof text. But the story of Onan says nothing of masturbation. Instead, the story is about a man who died, leaving his wife a childless widow. The dead man's brother was then expected to marry his widowed sister-in-law, have normal sexual relations with her, and enable her to have children. Although Onan was happy to have sex with his sister-in-law, he would practice coitus interruptus with her just prior to his orgasm and ejaculate on the ground rather than obey God and become a father. To argue against masturbation with Genesis 38:6-10 is as ludicrous as arguing for masturbation with Ecclesiastes 9:10, which says, Whatever your hand finds to do, do it with all your might.
For more reading on this see Pastor Mark's new eBook-
Porn Again Christian