joseph
40 is for any transformation:
40 years in the Midbar before we were transformed into a nation fit to enter Eretz Yisroel
40 days on HarSinai
40 makkos to transform a rasha into a tahor
40 days for a blob to become a fetus
40 melachos to create the mishkan (40-1 as in the case of makkos, the extra one has to come from the person’s own machshava)
40 seah in the mikvah to make a goy a Jew, a tamei into a tahor.
Mem (40) is the middle letter of the Aleph-Bais which the Boreh used to create smething from nothing. (i made this one up, the others have a mekor.)
40 posts on YW until the thread degenerates.