The lords provided protection and maintained order; the clergy looked after the spiritual welfare of society; and the peasants labored to support the 2 higher orders. Stated more pithily, the lords fought, the clergy prayed, and the peasants worked. ~ Rondo Cameron
Feudal society was a pyramid. At the top was the ruling class: accounting for less than 5% of the population, with the king at the top, through various nobles, to the lowliest knight.
The clergy was the only class that was not biologically self-perpetuating, at least in principle if not practice. The clerical order bifurcated into the regular clergy, who withdrew from ordinary community life into monasteries, and the secular clergy – priests and bishops – who participated in the community. In the early Middle Ages, the monasteries had greater prestige. The status of the secular clergy rose with the economic upswing from the 10th century onward, as towns revived, and church officials played roles in both civil and religious life.
The clergy had its own stratification, based upon the social standing of the individuals entering the institution. Those of noble heritage were often destined for higher positions, whereas folk from more humble origins might aspire to a parish priesthood or a clerical office within a monastery. Vertical mobility for clergy surpassed that of rural society but was much less than civil society in town.
Peasants hypothetically broke into 2 classes: free and servile, but these were not nearly as distinct as the terms imply. Chattel slavery, Roman style, gradually died by the 9th century, except for the household slaves of nobility. Peasants who worked the land – supposed freemen – suffered under conditions that rendered them practically servile. Truly free men were a real rarity.
The power of lords was modestly circumscribed. Serfs were bound to the soil, not the property of the lord of the manor.
As manorialism evolved so too the social status of the peasantry. Into the 10th century the rights and obligations of slaves and freemen became increasingly similar, as economic conditions constricted freemen, while slaves graduated to serfdom, which was a name change without much practical distinction.
Serfdom was declining somewhat by the time of the Black Death which reached western Europe in 1347. There was a progressive easing of servile restrictions, though not of the economic extractions that kept liberty out of reach. The French Revolution was a culmination of the trend toward ending servility in the legal sense.
Conversely, while servitude was withering in the west from the 12th century on, serfdom as an institution gathered strength in central and eastern Europe, where it persisted into the mid-19th century.