Original: The Council decides that the threat of Sauron is too great and that the best course of action is to destroy the Ring by returning it to Mount Doom in Mordor, where it was forged.
Simplified: The Council decides that the One Ring has to be destroyed, which will also truly kill Sauron forever. But the One Ring can only be destroyed if it is thrown into the volcano Mount Doom in Sauron's land Mordor, where the One Ring was made.