Prophet Muhammad (PBUH&HP) was the last messenger of Allah Almighty sent to human beings to guide them towards a more prosperous and meaningful life: "O Prophet! Indeed, We have sent you as a witness, as a bearer of good news and as a warner. and as a summoner to Allah by His permission, and as a radiant lamp." (33:45-46). 

You might be interested to know more details on his delegation (be' tha). So, follow us to find out more.

1. How did Prophet Muhammad (PBUH&HP) Receive his First Revelation?

Prophet Muhammad (PBUH&HP) was born into the tribe of Quraysh, one of the prominent tribes of Mecca. He was known as an honest and faithful man such that he was called Al-Amin [i], meaning trustee. 
He used to spend some hours alone out of town in Hira cave to worship, contemplate and reflect the state of people of that time and the aspects of creation. It was during one of these occasions that he received the divine message of prophethood. He was nearly 40 at that time. It was Rajab the 27th on 610 CE that the Archangel Gabriel (Jibreel) appeared before him and said: "Read." Muhammad (PBUH&HP) replied: "I am not able to read." This was repeated two more times. Then, the angel Gabriel recited the first verses of the Quran:

"Recite in the name of your Lord who created -
Created man from a clinging substance. 
Recite, and your Lord is the Most Generous –
Who taught by the pen -
Taught man that which he knew not." (96:1-5)

And, his mission started there.

2. How Was the Condition of the People in that Era?

According to Imam Ali (AS), Allah Almighty sent Prophet Muhammad (PBUH&HP) as a warner (against vice) for all the worlds and a trustee of His revelation. That was while the people of his time were following the worst religion. They resided among rough stones and venomous serpents, drank dirty water and ate filthy food, shed each other's blood, and did not care about their relationships. They worshiped and respected Idols, and sins were clinging to them [1].

3. Who Testified to the prophethood of Muhammad (PBUH&HP) First?

Imam Ali (AS) sometimes accompanied Prophet Muhammad (PBUH&HP) when he went to Hira cave. And, the day that the Archangel Gabriel appeared before the Prophet (PBUH&HP), Imam Ali (AS) was there, too. Prophet Muhammad (PBUH&HP) said to Imam Ali (AS) that: "O Ali, you see all that I see and you hear all that I hear, except that you are not a Prophet, but you are a vicegerent and you are surely on (the path of) virtue." [3].

Afterward, being perplexed by this happening, Prophet Muhammad (PBUH&HP) went home to describe what has happened to his wife, Khadija (AS). She (AS) was the first woman who testified to the prophethood of Muhammad (PBUH&HP). And according to the authentic resources, the first man was Ali (AS) [2]. Imam Ali (AS) has described the situation like this: "In those days Islam did not exist in any house except that of the Prophet of Allah (PBUH&HP) and Khadijah (AS), while I was the third after these two." [3].

4. How Did people react to Prophet Muhammad (PBUH&HP) Claim about His Prophethood?

In the beginning and according to divine guidelines, Prophet Muhammad (PBUH&HP) did not reveal his revelations publicly. Still, it was confined to a small circle of his family, close friends, and whoever he thought was eligible. In this period, the aim was to find real loyal fellows, although few. Of course, polytheists found about it, but they did not take it seriously [4].  

Three years later, Prophet Muhammad (PBUH&HP) began to preach to his clan members by receiving the command to "Warn the nearest of your kinsfolk" (26:214). But he mostly received ridicule and mockery. Allah Almighty ordered him not to give up and make his mission publicly known: "So proclaim what you have been commanded, and turn away from the polytheists" (15:94).

The rich people of Mecca saw their power and wealth in danger with the ideas that Muhammad's (PBUH&HP) new religion proposed like social equality, sharing the wealth with needy people, and rejecting idols. On the contrary, people of the lower classes, slaves, and women were those who embraced Islam very soon [4]. 

According to the details above, Prophet Muhammad (PBUH&HP) was chosen by Allah almighty at the time when humanity was at its dawn, and morality was long disappeared among humankind. He was the one who once more reminded human beings of the concept of humanity and the reason for creation.

Notes:

[i] In the "Age of Ignorance" (before the advent of Prophet Muhammad (PBUH&HP)), people did not trust each other much and did not care about the safekeeping of others' affairs. But, everyone in Mecca trusted Prophet Muhammad (PBUH&HP), and when they went to business travels, they entrusted their valuable goods to him. So, he was given the nickname "Al-Amin." And, this title continued to be used for the Prophet (PBUH&HP) after the emergence of Islam, too, although some people had become against him since he fought idolatry. 

References:

1. "Nahjul Balaqah", Sermon 26.
2.  Allamah Amini, “Al-Ghadir”, vol. 3, p. 236.
3. "Nahjul Balaqah", Sermon 192.
4.  Jafar Morteza Amoli, “Al-Sahih Min Sirat Al-Nabi Al-Azam”

Every day we meet several people at work, in the shops, at the university, in the neighborhood, or at parties and gatherings with whom we communicate and interact. Talking, telling jokes, shaking hands, touching or kissing usually happen in these interactions; but, is a Muslim allowed to do all these with whoever he/she wants? Or is he/she permitted to be exposed to such acts?  These and many similar questions are answered in Islam.

To clarify and form the relations among people, Islam has presented the concept of Maharim and the two categories “Mahram” and “non-Mahram” which sometimes serve as conditions, requirements, or the basis of several Islamic laws. Regarding the Islamic rules on marriage, these categories define who a person can and cannot marry. Likewise, when dealing with the Islamic dress code, i.e., explaining whom one must cover specific parts of a body in front of, the concept of Maharim is required.

Who is Mahram?

One’s Mahram is anyone whom it is permanently forbidden to marry because of blood ties, marriage ties or breastfeeding. However, a woman does not need to cover her hair and put on Hijab when she is in their presence.  A woman's male Mahrams fall into three categories plus her spouse [1]. Mahrams for a man are derived similarly. The Maharim for both, extracted from the verses of the Holy Quran (4:22-23) and (24:31), are listed below [1], and all other people and relatives are considered as non-Maharams.

Categories of Maharim

Permanent or blood Mahrams, with whom one is Mahram through blood ties:
parents, grandparents, and further ancestors;
siblings;
children, grandchildren, and further descendants;
siblings of parents, grandparents, and further ancestors (cousins and their children are not Mahram);
children and further descendants of siblings;
In-law Mahrams, with whom one becomes Mahram through marriage ties:
father-in-law, mother-in-law;
son-in-law, daughter-in-law;
stepfather (mother's husband) if their marriage is consummated, stepmother (father's wife) even if their marriage is not consummated;
stepson (husband's son) even if their marriage is not consummated, stepdaughter (wife's daughter) if their marriage is consummated[i];
Rada or "milk-suckling Mahrams," with whom one becomes Mahram because of being breastfed by her. When a woman breastfeeds an infant that is not her child for a certain amount of time under certain conditions, she becomes the child's rada mother and everything concerning blood Mahrams apply here, such as rada father/mother, rada sister/brother, rada aunt/uncle and so on. In English, these can be referred to as milk-brother, milk-mother, etc. [ii].

Maharim and Marriage

It is forbidden (Haram) to marry Mahrams, but one can marry non-Mahrams who have reached puberty. As explained above, Married couples are Mahram to each other. But unlike other Mahrams, the limitations and rulings on looking and touching do not apply to them; i.e., married couples are the only ones allowed to touch and look at the whole body of one another; even the private parts. 

Maharim and Social Interactions

Regarding social interactions, there are some rules according to the concept of Maharim:

Women and men are both required to keep their gazes downcast and should not stare at the other person when facing non-Mahrams or talk to them. Even Mahrams are not allowed to see certain parts of the body of each other (this will be discussed more under a separate topic “the Islamic rules on looking“);
When talking to non-Mahrams, the tone of voice should be serious, and the dialogues should be direct and as much as necessary. One should also avoid telling jokes and laughing loudly [iii];
Any physical contact (i.e., shaking hands, hugging touching) with non-Mahrams is forbidden (haram), except for curing patients. In this case, if a doctor of the same gender as the patient exists and can cure, then it is forbidden to refer to a non-Mahram doctor.
When being sole in a closed room (where no one else can enter, i.e., locked place), it is forbidden for a non-Mahram man to remain alone in the company of a non-Mahram woman. The Prophet of Islam (PBUH&HP) said: “No man is alone with a woman except that Satan is the third one present ” [2];
It is required (Wajib) to cover specific parts of a body in the presence of a non-Mahram according to the Islamic dress code. For men, this includes from navel to knee. For women, the clothing should cover their hair and body, but covering the face and the hands, from the wrist to the fingers, is not mandated [3].

Notes:
[i] sister-in-law and brother-in-law are not Mahram.

[ii] Refer to your source of emulation (Marja’ Taqlid) for more details and the rulings.

[iii] See the article on modesty.

References: 

1. Mahram and non Mahram
2. S. H. al-Amili, “Wasail al-Shia”, vol. 20, p. 131.
3. A. Aroussi Howayzi, “Tafsir Noor al-Thaqalayn”, vol. 3/589, T. 105.