Remove transformation of rest pose

Hi,
I can't understand the mathematical reason for the "Remove transformation of rest pose". Can you give me some hints?
Thank you very much.

SMPL_MODEL/lib/npModel.py

Lines 114 to 121 in 47a2280

    
           # Remove the transformation of rest pose 
        
           G = G - self.pack( 
        
           	np.matmul( 
        
           		G, np.hstack( 
        
           			(self.J, np.zeros([24, 1])) 
        
           			).reshape([24, 4, 1]) 
        
           		) 
        
           	)

	# Remove the transformation of rest pose
	G = G - self.pack(
	np.matmul(
	G, np.hstack(
	(self.J, np.zeros([24, 1]))
	).reshape([24, 4, 1])
	)
	)