At the beginning of Islam, the number of literates in the whole Mecca was about 17 people (1). In those times, it was even considered as a shame to be able to read or write (2). In the ancient times, people mostly weren’t able to read and literacy was the exclusive privilege of the royal families or rich people. However, in the Arabia, even the royal families couldn’t read or write. Once, Prophet Muhammad (PBUH & HP) wrote a letter to “Bakr ibn Va’il”, a large Arab tribe, and enjoined them to believe in Islam; but when they received the letter, they weren’t even able to read it (3).
In spite of these shameful circumstances, Allah al-mighty sent His most important apostle to the people with only a book as his miracle. The first verses of the Quran, revealed to the Prophet (PUBH & HP), are about reading:
Read in the Name of your Lord who created; (1) created man from a clinging mass. (2) Read, and your Lord is the most generous, (3) who taught by the pen, (4) taught man what he did not know. (5) [96:1-5]

Knowledge and Literacy in Islam

Muslims differentiate between the era before the Messenger (PBUH & HP) and the era after him based on peoples’ knowledge. We call the time before the rise of Islam “The Ignorance era”. 
The holy Prophet (PBUH & HP) taught people that knowledge is the criterion that sets them apart   . The Holy Quran says:
Say, ‘Are those who know equal to those who do not know?’ Only those who possess intellect take admonition (39:9)
About learning, the Holy Messenger (PBUH) says:
 Seek knowledge even if you have to go to China to find it. (4)
Imam Ali (AS) also highlights the Importance of knowledge in his speech with one of his companions:
O Komeil! Knowledge is better than wealth, because knowledge protects you. But for wealth, you have to protect it. Wealth and money get less when you spend them, but by using your knowledge or by teaching it to others you even get more knowledgeable … O Komeil! The ones who love wealth excessively, are like dead people (spiritually) even if they are alive (Physically). However, the spirit of knowledgeable ones will always be alive in the hearts of people even if their bodies are dead. (5)
The Holy Messenger (PBUH & HP) even considered learning as “Vajib” which means that learning is an obligation for every Muslim:
Seeking knowledge is an obligation for every Muslim, men and women (6)
One of the clearest signs that shows the Prophet (PBUH & HP) wanted everybody to be literate and knowledgeable is that he ordered the slaves after the Badr war to teach the children of Medina to read and write and in return, the slaves would be free. (7)

Keeping the Knowledge Safe

The Holy Quran says:
By the pen and what they write (68:1)
We all know that without writing, we weren’t able to communicate our thoughts and ideas with each other and we couldn’t keep them for future generations. In this regard, the Holy Prophet (PBUH & HP) says:
Keep your knowledge safe.
Some people asked:
How can we do that?
The Prophet (PBUH & HP) replied:
By writing it! (8)
Moreover, Imam Sadiq (AS) said to one of his pupils, Mufazzal ibn Umar:
Write and spread your knowledge among the people and if you were going to die, leave your writings for your children because there will be a chaos in the future and in those times, people will not find any peace except in their books (9)
He also said:
Keep your writings because you will need them in the future (10)
Imam Hassan (AS) would gather his children,his niece and nephews and tell them:
You may be considered as kids now, but it is so likely that you will be the elders of many groups and families in the future. Therefore, it is your duty to seek for knowledge. And if there are some people among you who cannot memorize their knowledge, they must write and put their writings in their houses and keep them safe. (11)

Carriers of Books

Action and knowledge are inseparable in the Islamic view. If you act without having enough knowledge and data about the work you’re going to do, you will spoil it and your efforts will be in vain. Imam Sadiq (AS) says:
The one who acts without having enough knowledge is like a passenger who goes on the wrong road. So they get farther and farther from their destination as they go faster and faster. (12)
On the other hand, knowledge without acting is also useless. Imam Ali (AS) says:
Knowledge without action is like a tree without fruit or like a bow without its string (13).
The Holy Quran also says:
The example of those who were charged with the Torah (Old Testament), then failed to carry it, is that of a donkey carrying books. Evil is the example of the people who deny Allah’s signs, and Allah does not guide the wrongdoing lot. (62:5)

Resources

1.  Fotooh al-Boldan, Pg.473
2.   Al-She’r va ash-Sho’ara, Pg.334
3.   As-Sahih fi sirah an-Nabi al-A’zam, Vol.1, Pg.49
4.   Vasa’il al-Shia, Vol.18, Pg.14, number 20 & 23
5.   Nahj al-Balaghah, Utterance no.147
6.   Kafi, vol.1, pg.3
7.   At-Tabaghat al-Kubra, vol.2, pg.22
8.   Bihar al-Anvar, vol.2, pg.151
9.   Kafi, vol.1, pg.52
10.   Kafi, vol.1, pg.52
11.   Kanz al-Ummal, vol.1, pg.752
12.   Tohaf al-Uqul, pg.362
13.   Mizan al-Hikmah, vol.4, pg.2841

Unity between Muslims is considered as a crucial matter in Islam. Thus, the Quran compares discordance and disunity among Muslims to “a pit of the Fire”: "And hold firmly to the rope of Allah all together and do not become divided...And you were on the edge of a pit of the Fire, and He saved you from it." (3:103). Looking at the former nations, we find them honored and glorious when they were united, but disgraced and vulnerable when they fell apart [3]. Hajj, as one of the obligatory rituals in Islam, is one of the ways which encourages unity among Muslim nations. Let’s see how.

 Every Muslim is Welcomed to Hajj, No Exception!

There is no other ritual, social, or political program in Islam greater than Hajj, where every Muslim from any corner of the world finds the chance to approach others and communicate with them freely. 
Besides, it provides the opportunity to strengthen the emotional, social, and religious bonds with other Muslims. Hajj is a social kind of worship that represents the glorious Islamic unity through its numerous participants of various nationalities, skin colors, languages, and sects who are like brothers (49:10). They have left behind the religious conflicts, and follow the same intention, perform the same actions, and wear the same outfit.   

Hajj Brings Muslims Power

In Surah Ma’idah, it is stated that coming together around Ka’aba makes Muslims powerful (5:97). In other words, the aim of Hajj for Muslims is not just performing some physical actions. It is to bring Muslims of different races and origins together to get acquainted, communicate with each other, initiate political, economic and cultural relations, and find themselves closer to each other despite their many differences. 

Besides, Islam calls “every” Muslim to Hajj, which means that everyone, regardless of origin and skin color, is invited to the land of Allah. It reminds us of what the Quran says; that there is no superiority except rightfulness and the most righteous, is the noblest in the sight of Allah (49:13). This is an important message, especially for the less powerful Islamic nations, causing them to feel more confident and encouraging them to communicate with other Muslims, which ultimately results in a more united Muslim society. 

Muslims Are Like the Hands which Help Each other

In a discourse that Prophet Muhammad (PBUH&HP) has given during one of his Hajj pilgrimages, he described Muslims as brothers, and like a single hand (a united community) when facing the enemies [2]. Emphasizing brotherhood among Muslims during Hajj shows that this ritual was a good representation of unity. Thus, Muslims are expected to support each other and be close to each other as they are during Hajj.

Two Axes of Solidarity in Hajj

During Hajj, Muslims learn and practice solidarity in two main areas:

1. Ideology and Principles

During Hajj, Muslims can exchange ideas with Muslims of other sects. In the early years of Islam when non-Muslims also went to Mecca for their religious rituals, Prophet Muhammad (PBUH&HP) took this opportunity to introduce Islam to them and exchange ideas with them to spread his message and find followers in other cities, too. In Hajj, many misunderstandings and ideological conflicts can be discussed among Muslims, and the real beliefs of different sects about the others can be clarified. Hence, the wrong prejudgments and hostilities can be rectified. According to Imam Sadiq (AS), Hajj is a means to gather all Muslims from east to west to let them get acquainted with each other and achieve consensus [3]. 

2. Social and Political Matters

Through the communications that Muslims have during Hajj, they find out the social achievements and national advances in other Muslim nations and might decide to follow their path. They also learn about the social problems and deficiencies of others and might find solutions by further cooperation. Moreover, they become aware of the real political situations of other Muslim countries, especially the difficulties that sometimes other countries impose on them. For instance, one of the goals of Hajj is to announce the support of Muslims for Palestinians and those oppressed in the world. This helps Muslims to become more united against common enemies of Islam.

To summarize, Hajj is a time that a Muslim finds him/herself in the accompaniment of millions of others who wear as simple as him/her and who repeat the same words as him/her as they move around Ka’aba. This is where “one” is transformed into the totality of ‘people’, establishing the universality of the Islamic community with the goal of approaching Allah. 

1. References:
2. Imam Ali (AS), Nahj-ul Balaqa, Infallible 192
3. M. B. Majlesi, "Bihar al-Anwar", vol. 21, p. 105. 
4. Shaikh al-Hur al-Aamili, “Wasa’il al-Shi’a”, vol. 11, p. 14