The lord granted land (as an inheritance) for the service to his vassal.
The vassal was obliged to participate in military campaigns on the side of the lord, he could also serve at the court of the lord, engaging in administrative or judicial activities. Military service usually lasted 30-40 days a year. When the lord was captured, his eldest daughter married or his eldest son was knighted, the vassal provided financial assistance.
The lord guaranteed his patronage.
Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.