Your absolutely right Believer, even rain water could have been a form of baptism{Although baptize means to submerge}to him and would not have made a difference if there is no true change of heart.
The Baptism of Fire is the result of judgment as in the verse of Matthew 3:12{Whose fan is in his hand, and he will thoroughly purge his floor, and gather his wheat into the garner; but he will burn up the chaff with unquenchable fire}.
The Fan refers to a shovel used for tossing grain into the wind so it can blow away the lighter chaff, leaving the good grain to one heap or pile.
The unquenchable fire refers to the eternal punishment of hell or the Lake of Fire.
God Bless!