Possible meaning for 'long' in 'not long for this world'

I have come across the phrase 'not long for this world' in many English novels, but it has always struck me as odd, as if a word or part of the sentence were missing. I visited numerous websites but all seem to focus on what the phrase means (I knew what the phrase meant already from context in the novels), not its structure, in particular the, in my eyes, odd use of 'long for'.

I am not sure if this is the right place to be asking this particular question, but where does 'long for' come from in this sentence? Is it some archaic use or form of 'belong'?

Thanks for any light you can shed on this!

The expression dates at least as far back as the 18th C., and perhaps even earlier. It appears to operate on the trope of long to a span of time.

It's related to the similarly literary he is not long in years (as a way of saying that he is young). To be long is to have an abundance of time.

The preposition for in the expression echoes the somewhat archaic sense of destiny, a sense that persists in the idiom They're in for it now (meaning that trouble - usually punishment - awaits them.). It also works on a simpler level, indicating roughly for the purpose of or usefulness in...

To be not long for this world, then, is to have not many days/hours/moments in store for use in the world of the living.

(To be long, in this sense, has little to do with belonging, which entered the language via the OE gelaeng (to accompany, be at hand). Long, meanwhile, comes from OE longe and shares etymological DNA with German and Dutch lang.

The modern pronunciations sound similar, but they're different beasts.)

According to Online Etymology Dictionary, "to be not long for this world" which means soon to die is from 1714:

The adverb is from Old English lange, longe, from the adjective. No longer "not as formerly" is from c. 1300; to be not long for this world "soon to die" is from 1714.

In "be not long for this word", be long means:

Take a long time to happen or arrive: 'sit down, tea won't be long'

As the above example shows, it is usually used in a negative sentence.