Why was the feudal class structure strict

The feudal class structure was a hierarchical social system where the king was placed at the top of the social order followed by the barons, the bishops or clergy, the knights and the peasants at the bottom of the scale. This system was very strict since the king, who was the most powerful and wealthy man in the kingdom, granted his lands to his nobles. Besides, each landlord or noble had to provide the king with knights in return of loyalty and protection in case of war. If the barons broke their oaths, the lands which had been granted by the king could be withdrawn.