https://youtu.be/60xpQ9bLIyQ (Batman attempts to sacrifice himself)
The Bat-Family are some of, if not the most, self-sacrificing individuals in comic books.
They will always put their mission before themselves, no matter how dire the consequences may be.
“Then, a sacrifice is the necessarily violent act by which something is made holy, that is partaking of yet another original violence. As we will see, sacrifice is oriented towards magic, towards divinity, she also directs herself towards the violence intrinsically embedded within it.”
The definition of a self-sacrifice is taking on the violence of an act for the betterment of humanity, in short.
Since Batman and his allies see it as their responsibility to protect the citizens of Gotham, they are willing to take any pain and suffering dealt onto the city into their own bodies, so that no one else has to feel pain.
This could be compared to Jesus’ death on the cross for the sins of humanity.
Much like Jesus, the Bat-Family takes on all this pain in order to better their world.
They understand that people are going to suffer, that's just human nature, but by putting themselves in the line of fire they can ensure that the only ones getting hurt will be them, and that is a cross that they are more than willing to bear.
This pledge to self-sacrifice could also be considered a baptism into the Bat-Family.
“Baptism is the Christian rite of passage par excellence. Its meaning is fully personal and yet entirely corporate as it embodies the doctrine of membership of the body of Christ. Christian baptism, our initiation into the dying and rising of Christ, is the concern of the entire [human] race; the sin baptism exists to counter is human sin at its most widespread and least individual. However, its cosmic nature does not make it any less personal.”
Anybody who wishes to work alongside Batman must be willing to risk it all for the betterment of Gotham.
In the comics there is an initiation ritual that Bruce makes each of his sidekicks swear to before he even lets them don a costume.
In this ritual you have to promise to uphold the rules of Batman and to listen to his demands (I'll expand on what some of these commands are later).
You make an oath to be a good follower of the bat, much like Christians undertake an oath to follow as best as they could in the footsteps of Christ.