Sounds like someone paying for protection.
As long as he/she knows Who's offering ...
Except that no money is changing hands, and none of the people being baptized is thinking he has any sort of guarantee against being injured or killed. Quite the opposite.
Getting ready to go into battle has a way of getting one's attention and focusing one's mind on the possibility of being about to meet one's Maker, and what one should do to be prepared for that.