Let's crack on:
The topic: a triumvirate that is the sin of Onan, masturbation, sexual sin.
Except of course Onan, although having become synonymous with masturbation, has nothing to do with the act at all!
Genesis 38 finds Onan, Judah's son, being required to father a child with Tamar, the widow of his brother Er. The intention was that a child, if male, would claim a double share of Er's estate - but if there was no heir then Onan got it all!
Onan, whilst having sex with Tamar, pulled out of the arrangement, and the act, and 'spilled his seed in the ground'. This act of coitus interuptus meant no heir and therefore Onan inherited. This is a story of greed and failure to discharge (no pun intended) one's duty to a dead brother. This is about engaging in a 'levirate' marriage ('levir' meaning husband's brother - literally marriage to one's husbands brother') - and not keeping the brother's side of the contract.
Onanism is regarded as the 'spilling of one's seed on the ground.' But this blanket term covers a multitude of acts and would that we left Onan to be the patron of pulling of of a deal for one's own ends than cloud the other seed spilling encounters (and a psycho-sexual counselling course done many years ago listed many such activities) that go on in the world!
Onan in failing to bring about the birth of an heir for Er gives birth to an exclusively 'male only' offence - that of 'spilling seed' - but it is not about spilling but about the not fulfilling of an obligation
So farewell Onan, let's send you off the the legal department and file you under the heading of 'broken contracts for self-gain' and move on to the real matter in hand!
Just to understand my approach to this whole 'sexual sin' area, I find my Bible listing but three sexual states:
Marriage: and here this is taken to mean the male/female relationship,
Fornication: the sexual act engaged with outside of marriage, and
Adultery: the sexual act of a married person with one who is not their spouse (and vice versa).
Now this is a simple account of the three sexual States of matter -not popular with some (I have received short shrift from many who dislike the label 'fornicator' and others for whom 'adulterer' was less acceptable to them than the act they were engaged in. We are a bunch of odd people us humans, aren't we? We are all happy until we call it what it is!). But, human nature and sensibilities aside, this is what the Bible tells us to work with - although some clever sort will point to concubines, plural marriage and the like as found in the Old Testament and the Ancient Near East (ANE) accounts - I'm not going to muddy the water any more than necessary: and it ain't necessary)!
I think this is a good place to park the bus for now - we'llcontinue with this after the Sunday services (and a celebration of our patron saint and a harvest celebrations) are done.
I hope this has been of some help and that the whole, when completed, will prove to be of some value.