User blog comment:Xilinoc/Ch. 639 - BABY,HOLD YOUR HAND 2/@comment-25121259-20150820171501

So, from what I understood, the right arm protects the present, the current system, hence why it stood on the Shinigami's side who are a representation of that system. On the other hand, the left arm is on the side of progress, hence it joined the Quincy side that wanted to change the current system.

So the chapter title is quite literal, seeing as there is a giant baby-like creature holding and swallowing a hand-like creature.