Benefit of full indulgence - it was believed that if any Christian died fighting for their religion, they would be sent to heaven even with sins
To achieve Christian control of the Holy Land - Jerusalem was an important hotspot for Christian pilgrims but under Saladin they were not allowed there
To gain land in the crusader states after defeating them and seizing land
To fulfil feudal duty in their lord’s army
To gain wealth from seizing possessions of any town defeated