When it comes to finding synonyms for the phrase "most fire and brimstone," you'll want to look for words that convey intense, passionate emotion. Some options might include "fervent," "zealous," or "ardent." Alternatively, you could look for phrases that emphasize the emotional or spiritual aspect of this language, such as "sinners' retribution" or "divine punishment." Other possibilities might include "hellfire and damnation," "fiery condemnation," or "wrathful judgment." Ultimately, the best synonym for "most fire and brimstone" will depend on the context and tone of your writing, as well as the particular emotions or ideas you want to convey.