Will the Sinlessness of Heaven Last Forever?

Every week, I answer a common question related to the end times. Today's is about how we can be certain that the sinless state of Heaven will be permanent if Satan fell without being tempted.

Question:

I think a lot about Heaven, and something has been on my mind for a while. I know we won’t have a sin nature in Heaven and Satan won’t be there to tempt us. But Satan himself fell without anyone tempting him, and angels have free will just like we do. How can we be certain that the sinless state of Heaven will be permanent this time?