few issurim carry the weight this one does in the way people talk about it. the torah’s first case is onan, who “let it go to waste” and was punished severely (bereishis 38:9 to 10). the mishnah in nidda (13a) speaks in extreme terms about anything that leads to emission for nothing. and the kabbalah sefarim call it one of the heaviest sins. but the details get blurry.

1. what is the actual issur and its source? is it deoraysa or derabbanan? and is the onan story about the issur itself or about refusing to build his brother’s house?

2. why is it so grave? is the severity about wasted potential life, about kedusha, about the thoughts that drive it? different sefarim give different reasons. what is the mainstream halachic reason?

3. the nighttime accident: a person asleep has no bechira. what is the halacha of keri that happens in sleep, not wanted at all? is that an aveira at all? does it need teshuva, tikunim, mikvah, or nothing? and does what a person did during the day, what he watched or thought about, change the answer?

4. practically, what should a person do afterward? people hear about mikvah, tikkun klali, fasting. which of those are halacha, which are kabbalah, and which are just made up?

bottom line: why is spilling seed treated as so grave, what is the reason underneath it, and what is the halacha when it happens in sleep with no fault at all?