First, the Traditions are not limited to the Messenger's words. Rather, they cover his entire life: all his actions, likes and dislikes, and approvals or tacit confirmations of what his Companions said and did. He lived for 23 years among his Companions as a Messenger of God. He taught them Islam down to its minutest details. He led the prayer five times a day, every detail of which was recorded, for he told them: "Pray as you see me praying." He fasted and explained all of its details to them, just as he did for alms-giving and pilgrimage. The essentials of belief and pillars of Islam—prayer, fasting, alms-giving, and pilgrimage—alone are the subjects of countless books.
Being a universal Divine system that includes everything related to human life, Islam has laws and regulations for individual and collective life: spiritual and material, social and economic, political and military, and all other aspects faced during one's daily life. He laid down principles related to all these. He constantly warned his Companions against deviation, and encouraged them to be deeper, more sensitive, and more careful servants of God. He told them about former nations and predicted future events. Abu Zayd 'Amr ibn Akhtab reported that there were times when the Prophet would ascend the pulpit after the dawn prayer and address the congregation until noon. He would continue to address them after the noon and afternoon prayers, telling them what had happened from the beginning of the world until that time, and what would happen from then until the Last Day. Such addresses would include information on the upheavals of the other world, the grave, the Resurrection, the Great Mustering, balancing people's deeds, the Last Judgment, the Bridge, and Hell and Paradise.
The Messenger commanded armies, heard and tried cases as a judge, sent and received envoys and delegations. He signed peace treaties, waged war, and dispatched military expeditions. He laid down rules of hygiene and principles of good conduct and high morality. His miracles number in the hundreds. As he set an example to be followed by Muslims, and because of the vital importance of Hadith in Islam as well as his Companions' love of him, his life was recorded from beginning to end.
The Messenger honored the universe with his Messengership, His servanthood to God, and his exalted, peerless personality. As honored witnesses of his life, the Companions recorded everything related to him. When they scattered throughout the lands conquered by Islam, new converts asked them to relate Traditions from the Messenger. They were so deeply devoted to him that they remained extraordinarily faithful to their memories of him.
Once during his caliphate, 'Umar passed by the house of 'Abbas, the Prophet's uncle, on his way to the Friday congregational prayer. A few drops of blood fell on his robe from the gutter. He became so angry that he pulled the gutter to the ground, saying to himself: "Who slaughtered an animal on this roof so that its blood should stain my robe when I'm going to the mosque?" He reached the mosque and, after the prayer, warned the congregation: "You are doing some wrong things. I was passing by such and such a wall on my way here, when some blood dropped onto my robe from the gutter. I pulled the gutter to the ground."
'Abbas was upset and sprang to his feet: "O 'Umar, what have you done!? I personally saw the Messenger put that gutter there in person." Now, it was 'Umar's turn to be upset. He said to 'Abbas in great agitation: "By God, I will lay my head at that wall's foot and you will put your foot on it to replace the gutter. Until you do that, I will not raise my head from the ground." Such was their devotion and faithfulness to the Messenger. 
The Messenger implanted such a zeal for learning in his followers' hearts that Islamic civilization, under the blessed shadow of which a considerable portion of humanity lived peacefully for centuries, was built on the pillars of belief, knowledge, piety, and brotherhood. In the lands through which the pure water of Islam flowed, innumerable flowers burst open in every field of science, and the scent diffused by them exhilarated the world.
Some of these flowers, like Ibn Hajar al-Asqalani, read in two or three sessions the entire collection of authentic Traditions compiled by Imam Muslim. Imam Nawawi dedicated himself so thoroughly to teaching and writing that he never married—he did not want to assign any time to anything other than knowledge. Imam Sarakhsi, a great Hanafi jurist, was imprisoned in a well by a king. During that time, he dictated his monumental 30-volume compendium, Al-Mabsut, to his students from memory. When his students told him that Imam Shafi'i, founder of the Shafi'i legal school and regarded by some as the second reviver (mujaddid) of Islam, had memorized 300 fascicules of Traditions, he answered: "He knew the zakat (one-fortieth) of what I know." 
The works of Ibn Hajar al-Asqalani, Ibn Jarir al-Tabari, Fakhr al-Din al-Razi, Imam Suyuti, and others cover so many volumes that when divided among the days of their lives, we can see that they wrote about 20 pages every day. We cannot study or even read during our lives what each wrote during his lifetime.
Anas ibn Sirin, son of Muhammad ibn Sirin, one of the greatest Tabi'un scholars, says: "When I arrived in Kufa, 4,000 people were attending Hadith courses in mosques; 400 were experts in Islamic jurisprudence."  To understand what it meant to be an expert in Islamic jurisprudence, consider the following: Ahmad ibn Hanbal, whose Musnad contains 40,000 Traditions chosen from among the one million in circulation, was not considered an expert jurist by Ibn Jarir al-Tabari. Nor was he given the same status as Abu Hanifa, Imam Abu Yusuf, Imam Shafi'i, Imam Malik, and the like. The fact that some did not consider such a great figure an expert jurist shows just what intellectual and scholarly heights a jurisprudent had to reach to be regarded as an expert.
The general atmosphere was extremely propitious for the development of both religious and secular sciences, especially the science of Tradition. Every Muslim strove to acquire knowledge of Islam and recognize its Holy Prophet fully. People had a great aptitude for literature and languages, for poetry was widespread during the pre-Islamic period. The Qur'an came, first of all, as an absolute and incomparable linguistic miracle. No literary or poetic expert denied its eloquence, and almost all of them gave up poetry after their conversion to dedicate themselves to the Qur'an and the Hadith. One of them, the poetess Hansa, became so deeply devoted to Islam that when her four sons were martyred at Qadisiyah, she praised God, saying: "O God, You gave me four sons, all of whom I have sacrificed in the way of Your Beloved (Prophet). Praise be to You, to the number of thousands."  That blessed woman found eight linguistic or poetic mistakes in a stanza of Hassan ibn Thabit, a famous Companion and poet. After the Revelation, she gave up poetry and focused on the Qur'an and the Hadith.
Life was quite simple in the desert. This enabled people to commit themselves to Islamic sciences. Also, they had very keen memories. For example, the Messenger once asked Zayd ibn Thabit to learn Hebrew; within a couple of weeks, he could read and write letters in it. Ibn Shihab al-Zuhri, Qatada ibn Diama, Sha'bi, Ibrahim ibn Yazid al-Nakha'i, Imam Shafi'i, and many others publicly said that they never forgot a word after they memorized it. They could do this after either reading or hearing something only once.
When Imam Bukhari arrived in Baghdad, ten leading persons in Islamic sciences tested his knowledge of Hadith and memory. Each recited ten Traditions, changing either the order of the narrators in a chain of transmission or the chains with each other. For example, the famous Tradition: "Actions are judged according to intentions..." has the following chain (in descending order): Yahya ibn Sa'id al-Ansari, from Muhammad ibn Ibrahim al-Taymi, from Alqama ibn Waqqas al-Laysi, from 'Umar ibn al-Khattab. When they were finished, Imam Bukhari corrected the chains one by one from memory and repeated each Tradition with its own sound chain of transmission. The scholars then admitted his learning and knowledge of Hadith. Ibn Khuzayma went so far as to say: "Neither Earth or Heaven has seen a second person as knowledgeable as you in this field."
Imam Bukhari never sold his knowledge for worldly benefits. When the ruler of Bukhara invited him to his palace to teach his children, the great Imam refused, saying: "Knowledge cannot be debased by being taken to a ruler. If the ruler desires knowledge, he should personally come to knowledge." The ruler replied by asking him to assign one day a week to his children. Bukhari refused again, saying: "I'm busy with teaching the Umma of Muhammad. So, I cannot waste my time teaching your children." The ruler exiled him, and this greatest figure in the science of Hadith spent his last days in exile.
 Muqaddima li-Usul al-Sarakhsi, 5.
 M. 'Ajjaj al-Khatib, op. cit. 150–1.
 Ibn Athir, Usd al-Ghaba, 7:90.