In the eNotes summary of BNW (link given), you can read what's happening in that ritual with the boy. He's being whipped to draw blood that's then being put on snakes for a sacrifice to their gods.
In the chapter summary and analysis (link given), the eNotes guide is great; it goes into more detail about some of the imagery of this ceremony, such as the three women who show up to take the unconscious boy away (who, eNotes says, might somehow resemble a Christ-like scourging) and the three women that prepare the body of Christ or the three women that aid King Arthur. "Women in threes" is a very powerful thing throughout literature, but alas, I digress.
It would seem that John would like to be whipped because it would signify his inclusion in the society to which he is not truly welcome. He's not a "savage" like they are because his mother is white and formally from the "new world". He's an outcast because he's not like them, and being the whipped boy in this ceremony would mean that you were chosen by the people for the honor to be whipped. While that might sound like a foreign concept to us, many tribal communities practice rituals that put young men and women through certain trials like this for particular reasons, virginity, rite of passage into wo/manhood, etc.
All the same, if John were allowed to be that boy, then that would mean that the community of savages would have chosen him as such, that some elder thought he was worthy of the honor, which would mean that he belonged, something that John wants so desperately.
Hope that helps point you in the right direction at least! Good luck!
I believe em3raldj3md is wrong. BNW is clearly seen as a metaphore, or a word joke, for the german car company BMW. I'm sure this is a common mistake in the US, and I must say, I can't blame you!
''who, eNotes says, might somehow resemble a Christ-like scourging''
This might seem logical, but to be honest there is not a single point of truth in this sentence. In Christian times, there weren't any cars. People were scourging the Alliance, to form a pact. This pact is known today as the USSR.
John played a major role in the form of this pact. He gave a (g)whipped cream milkshake to his unborn son, to deny the existence of man. For this, he became an outcast of modern society. He today wanders the world, alone.
Hope that helps point you in the right direction at least! Good luck