Excerpted from Brush Up Your Bible! by Michael Macrone
"And Er, Judah's firstborn, was wicked in the sight of the Lord; and the Lord slew him. And Judah said unto Onan, Go in unto thy brother's wife, and marry her, and raise up seed to thy brother.And Onan knew that the seed should not be his; and it came to pass, when he went in unto his brother's wife, that he spilled it on the ground, lest that he should give seed to his brother.And the thing which he did displeased the Lord: wherefore he slew him also."
-- Genesis 38: 7-10 (KJV).
You might think [yes we do] Onan's sin was "onanism," an eponymous English term for masturbation...yep, that's what I thought...Dok?...But such is not what the Bible tells us: Onan does "spill his seed on the ground," but... he doesn't "get there" by himself...he's not 'on his own' with his 'first (five-fingered) lover', oh no: Onan has been put on the spot by Jacob but only with respect to a tribal law of that time...tribal law...(or in modern terms a bloody Godsend [oh yes] for brother-in-laws everywhere provided that the sister-in-law was a bit of alright!): so...let's get this straight...though Er is dead, if Er's brother impregnates Er's widow then any resulting son will be taken as Er's...ahem...OK, we know that primogeniture (succession through the first-born son) was of supreme importance (then) so really he's compelled by duty...could be fun...no?
Follow the link...read the rest... excuse me while I go to the little boys room...