I think the Catholics invented this sin called "Onanism" based on the story of Onan in Genesis chapter 38.
Onan's older brother Er died childless. Onan's levirite duty was to marry his brother's widow for the purpose of producing a male heir. Onan married Tamar, but didn't want to give her any children, so he pulled out, "spilling his seed on the ground" and was condemned because of it. According to the laws of inheritance at that time, if Tamar bore a son, he would be considered Er's heir, even if fathered by Onan, and receive a double portion of the inheritance. But if Tamar were childless, then Onan would receive the entire inheritance.
I think most Christians understand that to mean that the reason he was condemned was because he cheated Tamar out of a child and any potential male child out of his inheritance. But some take to mean that contraception is a sin in any context.
Onan's older brother Er died childless. Onan's levirite duty was to marry his brother's widow for the purpose of producing a male heir. Onan married Tamar, but didn't want to give her any children, so he pulled out, "spilling his seed on the ground" and was condemned because of it. According to the laws of inheritance at that time, if Tamar bore a son, he would be considered Er's heir, even if fathered by Onan, and receive a double portion of the inheritance. But if Tamar were childless, then Onan would receive the entire inheritance.
I think most Christians understand that to mean that the reason he was condemned was because he cheated Tamar out of a child and any potential male child out of his inheritance. But some take to mean that contraception is a sin in any context.
