Why was Pope Gregory VII eager to help out Constantinople with the invasions of his lands?

Pope Gregory had the power to send knights to fight in defense of Christendom. This allowed him to mount an attack on the Seljuk Dynasty. After the Seljuks defeated the Byzantine army at Manzikert and seized Anatolia, the Pope called for â??Soldiers of Christâ?? to go to Byzantiumâ??s aid.