In the Christian New Testament and the Hebrew Bible, fire and brimstone is a vivid description of God's wrath. It's also used to describe a fiery church sermon invoking images of hell.
A fire and brimstone preacher focuses on God's judgment and the ultimate punishment for sin, in the hopes of inspiring church-goers to repent. The phrase originated in the King James translation of the Old Testament. Brimstone means "sulfur," an element many people associate with the sweet, burning smell that follows a lightning strike. Fire and brimstone is meant to evoke the inescapable heat and odors of a fiery eternity in hell.