Final answer:
Lords were rewarded with land and titles for being faithful to the emperor, which strengthened the feudal system's structure of mutually beneficial service and protection.
Step-by-step explanation:
Lords in the feudal system were rewarded for their loyalty to the emperor with land and titles. They received these lands, known as fiefs, from their sovereigns as a form of payment and incentive for military support and protection. This mutual exchange was a fundamental aspect of feudalism, where vassals provided military service and in return were granted the rights to the land which allowed them to generate wealth and maintain their own retinues. This system also worked with other entities, such as the Church, where bishops could be lords of their own lands. In some cases, through these lands, wealth in the form of tax revenues came primarily from peasant's production rather than the vassals themselves.
Contrastingly, direct tax exemptions were occasionally granted as rewards for particular services such as reclaiming abandoned fields, but this was not the standard reward for feudal lords. Throughout history, land was the most significant form of wealth and power, as we also see in the Roman Empire, where political power was explicitly linked to wealth through land ownership.
In summary, lords were given land and titles for their allegiance, which afforded them power and wealth, defining a classic feudal relationship between lord and vassal as well as overarchingly affecting the structure of medieval societies and beyond.