Why do pigul, nosar, and tame incur kares?

Question

As described in e.g. Rambam hilchos Pisule Hamukdashin chapter 18, there are bunch of things that render a korban invalid, and someone who eats from it gets whipped. However, there are three types of invalid korban that someone who eats gets kares: a korban that was prepared with intent to eat it beyond the specified time, a korban when eaten beyond the specified time, and a korban eaten by someone tame. (Others, that don't incur kares, are a korban that's tame, a korban prepared with intent to eat it in the wrong place, and an animal with a physical blemish.)

Why do those invalidations, specifically, incur kares, when other invalidations don't? I'm seeking a taame-hamitzvos reason, not a how-do-we-know (what's-the-d'rasha) reason.

Answer 1

I don't know if he had a source, but a Rebbe of mine - Rav Yitzchok Fruchter of Jerusalem - explained this concept at various times.

There are three types of invalid korban that someone who eats gets kares: a korban that was prepared with intent to eat it beyond the specified time, a korban when eaten beyond the specified time, and a korban eaten by someone tame.

These 3 cases are done for the sake of doing a Mitzva.

The person knows he can't finish it on time - or the time has already passed - but he feels that it's a big Mitzva to finish eating this Korban instead of burning it.

Similarly, the impure - Tame - person is trying to help eat the Korban so it doesn't go to waste.

This type of being more righteous than the King (who explicitly forbade it) warrants a more severe punishment, to prevent people from doing these Mitzva-Aveirot. Otherwise they may just decide that it's worth getting lashes in order to fulfill the important Mitzva of eating the korban.