What is a Footstool?
2 Chr 9:18. Kings and other rulers sitting in state required a stool upon which to rest their feet. The divine glory, which resided symbolically in the holy place between the cherubim above the ark, is supposed to use the ark as a footstool. 1 Chr 28:2; Ps 99:5. So the earth is called God's footstool by the same expressive figure which represents heaven as his throne.
Bibliography Information Schaff, Philip, Dr. "Biblical Definition for 'footstool' in Schaffs Bible Dictionary". bible-history.com - Schaff's