Quote Originally Posted by Redefiner
Okay, this is a spoiler, and I don't know how exactly to tell you this without completely spoiling it, then again...it's kind of expected.

Beat through Sin and eventually, all the temples, including Bevelle, will be re-unlocked.

For more details and a slight spoiler, I guess:
(SPOILER)Beat through Sin until you beat Seymour the last time. Then go back outside of Sin, speak to Tromell at Guadosalam, and that should open all the temples up, including Bevelle. I'm not sure if this can be done earlier, cuz I just thought about every single little thing that I might have forgotten before fighting the Final Boss.
Wrong, all the temples except Bevelle's will be unlocked. Bevelle is inaccessable at that point except for the walkway leading out of the city where you fought Seymore. You only get the one oppertunity where you are in Bevelle temple to get the destruction sphere treasure and that's it. That's why they put it in plain sight. If you didn't get it the first time I'm afraid you'll just have to start over as there really is no way to get back in there.