The social structure which grew up in the early Middle Ages was clearly a product of the disorders of this period.
Much of society was organized on the local level.  Localities had to be as self-sufficient as possible; because they had relatively little contact with one another.
While a few groups, like soldiers, pilgrims, and merchants, might move around a good deal, the majority of the population remained close to home.  Most men and women lived their whole lives within sight of the village where they were born.  During the Middle Ages, particularly in the earlier centuries, most people led a fairly isolated existence, largely unexposed to the intellectual crosscurrents which help bring about change.
A medieval bishop characterized his society as being divided into three groups: "the men who work, the men who fight, and the men who pray."  These were the three great social classes of the medieval world.
Estates:  the name which people of the Middle Ages applied to these social classes.
(1)  First Estate = the Christian clergy (the men who pray)
(2)  Second Estate = the Warrior Aristocracy (the men who fight)
(3)  Third Estate = the rest of the population (the men who work)
The first two estates were the 'upper classes' or elite of medieval society.  Although they comprised a relatively small percentage of the population (never more than about 5%), they dominated that society.
Throughout the Middle Ages, most (though not all) members of the third estate were agricultural laborers known collectively as peasants.  Among the peasants there were three basic sub-groups (serfs, slaves, and free peasants).  It was largely their work that supported the Churchmen and warriors.
As the Middle Ages progressed, a new social group appeared on the scene -  townspeople who who lived in the fast growing towns and cities of late medieval Europe.  Despite great economic and social differences within the ranks of townspeople, medieval society grouped them in the third estate, along with the peasants.  Although they remained vastly outnumbered by the peasant population, their growing economic and political strength soon made them the dominant sector of the medieval working class.
When the bishop characterized medieval society, he referred to the men who worked, fought, and prayed.  This merely illustrates his masculine orientation.  Actually, women belonged to all three estates, including the clergy (albeit their role as members of the church was fairly narrow.)
The bishop was also referring to Christian society.  During the Middle Ages, virtually all of Europe converted to Christianity.  The relatively few non-Christians who were permitted to live among the Christian majority were, at best, barely tolerated.  They were social outcasts who did not really fit into any of the three estates.
Most of the non-Christians whose presence medieval society usually tolerated, but never welcomed were Jews.  A few, primarily in Spain and southern Italy, were Moslems.  Both groups were used as scapegoats for anything which went wrong in medieval society.
Examples of medieval intolerance:
(1)  At the beginning of the First Crusade (c. 1095), crusaders starting out for the Holy Land massacred Jews in France and Germany.
(2)  In the mid-fourteenth century, many European Christians blamed the Jews for the great plague that devastated Europe and which may have destroyed more than a third of the European population. Several of their explanations for the plague worked to the distinct disadvantage of the Jewish population.  
(a)  It was God's judgment against a society that would allow non-believers to live among Christians.
(b)  The Jews were causing the plague by "poisoning the wells." 
No matter that that Jews were dying from the plague every bit as quickly as Christians or that many who drank from those supposedly poisoned wells never got sick.  In what was considered 'just retribution,' many Jews were slaughtered by the frightened Christian majority.
Pogrom:  a word which refers to a massacre of the Jewish population.
Although the life of a warrior in the Middle Ages tended to be far better than that of a peasant, by modern standards, it would be considered quite primitive.  One need only remember how many things we take for granted simply did not exist during the Middle Ages.  They were no more available to the wealthiest king than to the humblest worker.  

Medieval Warrior

The medieval warrior was a member of the Second Estate.
Knight:  the English word for the heavily-armed, mounted warrior of the Middle Ages.
Knighthood:  the state of being a knight.
The usual candidate for knighthood was a young man who had been born into the warrior class and whose father had been a knight before him.  Only on fairly rare occasions did a commoner from the third estate win knighthood.
Knighthood was an exclusively masculine institution.  A women could not become a knight.  In fact, for a woman to wear men's clothing was regarded as unnatural and could get her in serious trouble with society and the church (witness the case of  the maid of Orleans, Joan of Arc. One of the charges brought against Joan was the wearing of men's clothing.)
Most Romance languages had a term meaning "knight" which was related to their word for "horse" - the animal with which the the medieval warrior was most closely-associated.
(1)  Chevalier (French)  (Horse = cheval)
(2)  Caballero (Spanish)  (Horse = caballo)
(3)  Cavaliere (Italian)  (Horse = cavallo)
Chivalry:  a word, derived from French (cheval, chevalier); it refers to that whole code of honorable conduct in accordance with which a warrior was supposed to shape his actions.  Knighthood is often used as an English synonym for chivalry.
The institution of knighthood probably grew out of the primitive German ceremony - described by the Roman historian Tacitus - in which young warriors, upon coming of age, were given their arms in the presence of the tribe, making them full-fledged members.
Many aspects of medieval society can be seen to have their roots in either the Roman or German past.  Knighthood is just one illustration of this important fact. 
Over the course of the Middle Ages, knighthood, like almost everything else, underwent an evolutionary process.  The whole concept of the knight and his duties to society grew increasingly complex.
In the early period, the knight was called upon to be loyal to his lord; and faithful to his vassal.  He was to show courage (prowess) in battle.  He was to defend his own rights and honor; as well as the rights and honor of family members.  Thus, early knighthood was almost exclusively a military ethic which centered around the individual and his family.  The only outsiders to whom he owed a duty were his lord and his vassal.  In this early period, knightly training was also rudimentary.  While a person might spend a short period of time in some other warrior's household, leaning the rudiments fighting, much of his real training was what we might call “on the job.”  The young warrior would be introduced to battle where he could sharpen his skills by actually fighting the enemy.
Accolade:  tap on the shoulder with the flat of a sword making a man a knight.
Forces which helped reshape the ideals of the medieval knight as the Middle Ages progressed:
(1)  Christianity
(2)  Changing view of women
As the Middle Ages progressed, an ever more elaborate code of chivalry infused with Christian values tried to impress upon the knight that his obligations extended beyond just himself, his family, and his lord or vassal; that in fact, he owed various duties to the larger society in which he lived.  In particular, chivalry came to embody his obligation to promote the interests of the Church, to spread the faith, and to protect the poor, the defenceless, and the downtrodden of society.
Around the year 1000, the new rules were set forth by the Church in two remarkable documents:
(1)  The Peace of God (pax dei): listed the non-combattants of society whom the knight was not to harm.  These included widows, orphans, travellers, merchants, priests, pilgrims, and peasants.
(2)  The Truce of God (truga dei): specified certain days of every week, and whole seasons of the year when all fighting was to cease.
Although often ignored in practice, these rules helped define chivalry in its more developed state.  All of these changes reflect Christian influences on the code of chivalry.
Later in the Middle Ages, the Church also decreed that it was part of the knightly function to participate in crusades, both to protect and to spread the faith.
Crusade (from the Latin word 'crux' meaning 'cross'):  holy war that Christian society conducted not against pagans and the followers of Islam, but also against heretical Christians.
Another significant force which helped alter the concept of chivalry was the improving status of women in the Middle Ages.
Early medieval society, like many other past societies, did not have a particularly high regard for women.  Nor did Christian theory help much to improve their standing, since it tended to view women in a rather unfavorable light - as the temptress, Eve, whom men should avoid as much as possible.
Dowry:  the property that a woman brought to marriage; an important consideration in estimating her "value".
However, once again over the course of centuries, there were counter-currents which did tend to improve the status of women:
(1)  The important role aristocratic women played in a rough-and-ready society where warriors were often away fighting or had died young
(2)  The cult of the Virgin Mary
(3)  The cult of Courtly Love
The lady of the manor played a major role in running the household and even the estate, particularly when her husband was absent, injured, or dead - all of them fairly frequent occurences inn the Middle Ages!  In an age of disorder, as in any frontier society, the demands on everybody tend to be greater.  Consequently, both men and women are required to pull a heavier load.  This often results in a rise in the status of women, society's way of acknowledging their contribution.
In the early church, Mary had not been the highly important figure she became during the Middle Ages.  By raising her to a leading position in Christian doctrine, the church helped improve, by association, the image of women as a whole.  There was now a new Christian image of women--Mary, the compassionate mother--to counter the older image--Eve, the temptress who leads man into sin.
Courtly love was a "secular idealization" of women.  It created the powerful image of the "knight's lady," a woman whom the knight was to place upon a pedestal and in whose name he was to do his great deeds.  Starting around the 12th century, this image began to permeate the chivalric literature.  Spread by the troubadours, the cult of courtly love called upon the knight to adore, honor and serve a particular lady; and, to be courteous and good to all noble ladies.  (Note that the words "courteous" and "courtly" derive from this phenomenon.)
The object of a knight's courtly love was not ordinarily his own wife.  Not infrequently, it was somebody else's wife (a fact which has led one historian to characterize courtly love as "adultery raised to the level of social obligation!")  This could often lead to marital problems: witness the most famous "love triangle" of the Middle Ages, the case of King Arthur, his wife, Queen Guinevere, and her "courtly lover," Sir Lancelot, which destroyed the king's friendship for Lancelot and brought down the Round Table.
 Eleanor of Aquitaine:  the strong willed duchess who married the king of France, then deserted him for the younger and more handsome king of England, Henry II.  Eventually, she mothered two of England's most famous (though by no means most competent monarchs--Richard the Lionheart and his brother, John; and, when they came of age, plotted with both of them against her husband, Henry.  She played a key role in pioneering and promoting the idea of courtly love, by gathering around her minstrels and troubadours who composed the romances of chivalry that became the embodiment of courtly love.
Despite improvement in image and condition of women, widowhood remained the freest time in a woman's life - a period when she was not under the control of some male - and noblewomen often paid for the right to remain widows when their lords or relatives tried to marry them off for a second or third time!
 As the medieval period progressed, training for knighthood became more elaborate and institutionalized.
There came to be three stages through which a knight was expected to pass:
(1)  Page (age 7-14)
(2)  Squire (age 14-21)
(3)  Knight
Training was usually conducted in someone else's household.  Thus, the would-be knight had to leave his home at a relatively young age (approximately 7).
Only while he was still a page could a future knight be required to do menial tasks.  At that point, it was considered good discipline.  Later on, such tasks would be considered to be below him.
Important Aspects of knightly training:
(1)  use of weapons
(2)  riding
(3)  hunting
(4)  falconry
(5)  gaming (!!)  (A warrior had to know how to gamble like a gentleman!)
In some relatively refined households, there might also be some training in poetry, music, and dancing.
Rarely would the education including reading and writing, for which the warrior class saw little use throughout most of the Middle Ages.
Even the ceremony of becoming a knight became much more elaborate.  It was the secular equivalent of ordination to the priesthood.  A young man dressed in special clothes, fasted for 24 hours, and spent a night in prayer and contemplation before the accolade was administered.  The higher ranking the person to administer the accolade, the better.
There was also a ceremony for stripping a man of his knighthood, in which he was declared "dead to the world," not dissimilar to what happened in the ceremony conducted for lepers, the most despised segment of medieval society.
Not all squires became knights.  While some failed to complete the training, others were simply not wealthy enough to take on the mantle; in fact, the elderly squire became a medieval literary stereotype.