The contingency is only "till all is fulfilled" --- the generation is guaranteed to last at least that long.Explain this to me again because I'm slow. To tell them that that generation (however one defines "generation" but that's another can of worms) would not pass away until all that He described had come to pass...that's a very certain thing. As in, "You can bank on it." So where's the conditionality/uncertainty in that? I don't see any at all.
But it does not guarantee that the generation will last forever and ever, even after all is fulfilled.
So it has to use the subjunctive mood that depends on more info (and in this verse, more info is given --- till all be fulfilled.
It should be noticed that both clauses ......
Luke 21:32 KJV
(32) Verily I say unto you, This generation shall not pass away, till all be fulfilled.
(32) Verily I say unto you, This generation shall not pass away, till all be fulfilled.
.... are both in subjective mood.
Meaning that while they are guaranteed to not pass away UNTIL ALL BE FULFILLED, that guarantee is still only a possibility/uncertainty after all be fulfilled.
Anytime the subjective mood has a contingency clause after it, (usually after an if, until, then, etc).
That clause "till all be fulfilled" is what modifies it at least to that point, but still not guaranteed beyond that point.
If the verse had another clause after "till all be fulfilled" that modified it even more, such as .......
Verily I say unto you, This generation shall not pass away, till all be fulfilled, then I will establish you before Me forever.
........... would give more info of the contingency (in this last case they will NEVER pass away).
But as the verse stands, the only guarantee is that they will not pass at least until all be fulfilled.
So the possibility/uncertainty is still there that they could pass away or not, but only after all is fulfilled.
The verse is not trying to establish that the generation will never ever ever pass away, but only that the generation will remain at least up until all is fulfilled.
After that point, this verse still leaves it up in the air as to whether they will ever pass away.
Long story short, additional "context" in the verse determines what the contingency/stipulation/condition is.
In this case the additional context providing that contingency/stipulation/condition is "till all be fulfilled".