You have to pull the levers on either side of the statue. Walk to the sides and go to the upper level to find the levers. Once you get one of the arms moved away from his chest, grab a stone block to stop the lever from moving. Pull the lever on the other side, now quickly go back to the center and pull the lever in front of the statue. Both arms should be moved away from his chest. Use the hanging coffin to break through the chest of the statue.