What does “You must long for the next life” means?

Question

This is a phrase from the new episode of TV show Game of Thrones. Some context: Jaime Lannister (a knight) is speaking with High Sparrow (a priest) during funeral ceremony. They don't like each other.

High Sparrow said:
Do you know why we use these stones? To remind us not to fear death. We close our eyes on this world and open them on the next.

Jaime answered:
You must long for the next life.

I don't understand, what does it means. Is it an idiom (the whole phrase) or just special meaning of "must long"? Does it mean threat or insult or anything else?

Answer 1

In colloquial terms, Jaime is saying:

You must really, really want to die (and experience whatever comes after).

To long is defined as:

to have a strong wish or desire.

according to the Oxford Web Dictionary.

It has a similar meaning to want, but is much stronger. As Lambie mentioned, it is almost an exact synonym of "yearn."

You should note that Jaime is being sarcastic when he says this. He's making fun of High Sparrow's attitudes towards death.