The concept of responsibility in Islam covers all the aspects of human beings and considers different situations one may encounter in his/her life. Islam is not only a religion but also a life plan; a divine plan that addresses all the humans throughout the history of humankind. Since religion, as a plan deals with the daily life of humans, it has illustrated the tasks and responsibilities in Islam of humans.

These duties can be summarized in four items: 

The rights that God has over humans;

The rights that one has over himself;

The responsibilities towards other humans;

And, the responsibilities towards other creatures in this world.

These four categories will be discussed under separate topics each considering one responsibility in Islam. Here the focus is on the humans’ responsibility in Islam towards God.

The Most Important Right of Allah over Humans and Their Responsibility in Islam

According to Imam Sajjad (AS), the rights that God has over human beings, which are the most important rights over everybody, are to know that we are His servants, to pray Him and not ascribe any partners to Him [1]. This means that we have two main responsibilities in Islam towards God: first, to recognize and believe in God then, practically demonstrate it. 

To recognize God and to believe in Him

The first thing is to accept the existence of the one true God and to recognize all his divine attributes such as very powerful (Qadir), the provider (Razzaq), generous (Karim), etc.

By knowing these attributes and then believing that they are unique to God, one will be more successful in his duties responsibilities in Islam towards God [i]. For example, knowing that God is the only provider (Razzaq) in the universe, a true Muslim does not worry about livelihood, nor he\she will be greedy for more wealth. He\she knows that if he\she works adequately according to his\her capacities, he\she will be provided with the sustenance that God has reserved for him\her. 
Imam Ali (AS) has advised his son Imam Hassan (AS) to recognize God since it is a duty over every human being: “He is One Allah whom we should all recognize and worship” [2].

Then, Imam (AS) enumerates some of the attributes of God that a Muslim should believe in [2]:

“Nobody is a partner to Him in His Domain”;
 “He is Eternal, has always been and shall always be”; 
“He existed even before the Universe came into being, but there is no beginning to His Existence”; 
“He shall remain when every other thing shall vanish, and there shall be no end to His Existence”; 
“His Glory and His Existence is so supreme, pre-eminent, transcendent, incomparable and excellent that it is beyond the grasp of intellects”; 
“No one can understand or visualize Him.“ [2].

To Verbally Admit to the Unity of God as a Responsibility in Islam  

To recognize God and to believe in Him deeply in the heart are not enough; one should also say that he\she believes in God; otherwise, no one will be aware of his\her belief if it is not declared. That is why one should pronounce two testimonies (Shahadatain) to become Muslim.

In Surah Fatir, it is said that “To Him ascends good speech” (35:10), which means that the verbal admission to God is appreciated and is surely beneficial. But, it should be accompanied with good deeds and obedience to God to be more valuable: “and righteous work raises it.” (35:10). 

To Worship God and to Obey his Commands

Indeed, demonstrating the belief in God in practice is as important as believing in Him. If a child loves his\her parents but ignores their expectations and advice, he\she, in fact, does not respect them and the parents will not believe the his\her claim of having affection for them.

The same happens between a Muslim and God. A Muslim who ignores God’s commands, which are beneficial to him\her, does not truly believe in Him. Otherwise, he\she knew that everything that God has ordered to is to help him\her to live a better life, to improve and to reach the perfection that he\she merits.

According to Imam Ali (AS) [2], after accepting the facts mentioned above about God, a Muslim’s behavior should be like that of a person who realizes God’s superior status and power. He\she should try to gain His blessing through prayers and obedience, fear His wrath as well as His Punishments and feel him\herself absolutely in need of His help and protection [2]. 

In the Quran, it is stated that humans are created to worship God  (51:56). Prayer and worship of God are duties over every Muslim as they remind him\her of the his\her creator and the fact that there is a reason to be in this world. 

Another practical duty is to obey God’s commands that are mentioned in the Quran or explained in the narrations from prophet Muhammad (PBUH&HP) and Imams (AS). Simply said: to do what is obligatory (Wajib) or advised to (talk pleasantly to others (2:83); to do good to others (16:90); to fast (2:183) and pray (4:103); etc.) and to leave what is Forbidden (Haram) (talking behind back of others (49:12); wasting water and nutrition (7:31))2.

Briefly, there are three main duties over every Muslim about God: to recognize Him, to declare the admission to Him, and to obey and worship Him. Duties of a Muslim towards him\herself and his responsibility in Islam, other people, and other creatures will be discussed in the next parts of the article.

Notes:
[i] Recognition and belief are two different concepts. The recognition of God means to accept His existence and all His divine attributes, while the belief in God means to have faith in Him. 

[ii] The two other categories of acts according to Islamic jurisprudence are: Recommended (Mustahab) acts and Detestable or abominable (Makruh) acts. Recommended (Mustahab) acts are those practices which are not compulsory in Islam, but a believer prefers to do it for God’s satisfaction. Detestable or abominable (Makruh) actions are not subject to punishment, but a believer abstains from them for God’s satisfaction.

References:

1. Imam Sajjad (AS), Treatise On Rights (Risalat al-Huquq).
2. Nahj al balagha, Letter 31.
    

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”