-"The image's belly and the thighs of brass,
We know from the history that the third kingdom of brass, the one to follow Persia, was the Grecian Empire.
The Greeks , symbolized by the belly, liked to eat & feast. The Greeks were also interested in philosophy, religion and spiritual things . And it is held by almost all religious that the seat of the spirit is in the belly.
As Jesus Himself said, "Out of his belly shall flow rivers of living water. (This spoke He of the Spirit.) -- John 7:38,39