I think "do not keep until the following morning any part of the animal killed at the Passover Festival" means that every part of the sacrificed animal must be consumed or destroyed before the morning comes.

Until is the moment something ends. He was watching TV. His mother came home. (right now) He stopped watching TV. Imagine you were playing basketball and you stopped at 2:00pm, you would say; "I played basketball until 2:00pm." As far as the first sentence goes it does mean that everything part of the animal has to be gone by the morning. Old English, especially Biblical writing tends to be written in a very awkward manner than you generally hear anymore. If someone wrote this tomorrow it would simply say; "The animal killed at the Passover festival must be discarded before dawn." or something to that effect.

I hope I will make my answer simply because I am a Jew. You should not keep any part of the animal killed at the Pesach Festival so it should be disposed before the following morning. Until is a preposition for 'up to the following event'. He stopped watching TV when his mother arrived home. He watched TV until his mother came back. For example, about a job position in a company. Look at the sentence, "review of applications will begin immediately and continue 'until' position is filled." that means the job position will be given to one of chosen applicant when they finally decide who is the best for this job. I hope it helps you!

1. Do not keep = do not keep It means it shouldn't be there the following morning. What happens to the animal is not explicit stated. 2. It is not explicitly stated what he was doing when his mother came home. We only know he was watching TV up until the point she came home. We don't know if he stopped or continued watching after that. All in all, stop adding meaning to words. until = 到 do not = 别 There is no need to add any more meaning.

The reference, of "until" in the setence "he was watching tv until his mother came back" literally means. The boy was watching tv, but when his mother returned home/came back, he turned the tv off.