Mark 9:49. "For everyone will be salted with fire."

This comes after Jesus' teaching that if our hands or our eyes are causing us to sin, it is better to be rid of them than to be thrown into hell, where the fire is not quenched. After this, Jesus goes on to say salt is good, unless it loses its saltiness. So if we will be salted with fire, and salt is good, then Jesus is saying it is good to undergo the sufferings of the fire now, and retain their benefits.

Fire is purifying, when used at the right time and in the right way. Jesus is telling us to let ourselves be purified and seasoned by the fires, or sufferings, that God gives us here, and to retain that seasoning, hold on to it, stay fired up in His cause. If we don't accept the purification from our sufferings while on earth, we will not be saved, and we will suffer eternal sufferings that can no longer purify us. But if we accept them here - if we walk into the fire and let it cleanse us, if we learn the lessons of our suffering and let God lead us through them - then we will be purified, seasoned vessels, able to do His will on earth.