I don't know if you still need this or whatever, and this may be a spoiler, but here's what Garland says at the end of the game.
(SPOILER)"Remember me, Garland? Your
puny lot thought it had defeated me.
But, the Four FIENDS sent me back 2000
years into the past.
"From here I sent the Four FIENDS to
the future. The FIENDS will send me
back here, and the Time-Loop will
go on.
"After 2000 years, I will be forgotten,
and the Time-Loop will close. I will
life forever, and you shall meet your doom!!"
At this point Garland turns into Chaos, and if you're not prepared, he will mulch your party.
I just finally beat the NES version myself. I've seen the ending countless times, but I was never the one actually playing the game... so... victory for me! yay!