According to some this refers to the purifying fire of the trial whereby the disciples still have to be hardened.1 With others it can be argued that “fire,” so shortly after the repeated mention of “fire” in verses 44, 46, 48, must refer to the destroying fire of punishment intended there for all who caused little ones to stumble and fall. “Everyone” here is then referring to “everyone who ends up in Gehenna”: there the fire does not end, for everyone is (then) “salted” with fire.2
49 For everyone will be salted with fire.