Indeed Allah conferred a great favour on the believers when He sent among them a Messenger (Muhammad Sallallahu 'alaihi wasallam) from amongst themselves (being human, people can easily benefit from his distinguished qualities), reciting unto them His verses (by means of these Qur'anic verses, inviting them and advising them) and purifying them (of sins and correcting their conduct) and teaches them the Book (Qur'an) and Al-Hikmah (his Sunnah), before which they were in manifest error. [Ale-'Imran 3:164]
In the context of the above verse, Sheikh Sayyad Sulaiman Nadavi Rahmatullahi 'alaihi writes (in the preface of a book about Sheikh Muhammad Ilyas Rahmatullahi 'alaihi and his religious movement) that Rasulullah Sallallahu 'alaihi wasallam was given the following Divine obligations of prophethood: Invite towards Allah by reciting the verses of the Qur'an, to purify /people's undesirable traits, and to teach them the Book and Wisdom (Sunnah).
It has been substantiated by the Qur'an and Ahadith-e-Sahiha (confirmed traditions) that the Ummah (followers) of the Last of the Prophets, Sallallahu 'alaihi wasallam, was Divinely deputed for the guidance of all peoples (nations) of the world.
Allah Subhanahu wa Ta'ala says: ...
(O Muslims) You are the best of the peoples, you have been sent towards mankind, to enjoin good and forbid evil. [Ale-'Imran 3:110]
This verse clearly implies that the Muslim Ummah is the deputy to the Prophet, in his ordained obligations of inviting towards righteousness, enjoining good, and forbidding evil. Hence, the obligations entrusted to Rasulullah Sallallahu 'alaihi wasallam - invitation through recitation of the Qur'an, purifying people of undesirable qualities, and teaching the Book and Wisdom - became the prime responsibilities of Muslim Ummah as well.
Therefore, Rasulullah Sallallahu 'alaihi wasallam taught his Ummah to spend their life and wealth in inviting towards Allah, learning and teaching Divine knowledge, Remembering and Worshipping Allah. The Sahabah gave preference to the above deeds over all worldly preoccupations. They were trained to practice these A'mal (actions) under all circumstances with complete dedication, patience, and forbearance withstanding all forms of difficulties and hardships. And they were taught to benefit others by sacrificing physically and materially.
In compliance with the command: ...
And strive hard in Allah's cause, as you ought to strive [Al-Hajj 22:78]
The Sahabah strove in the manner of prophets with piety, austerity, discipline, self-sacrifice, and giving preference to others. Thus, an environment was created in which emerged models of excellence, who became the elite of the Ummah. The era in which the deeds of Rasulullah Sallallahu 'alaihi wasallam were collectively practiced by the Ummah was declared to be the Khair-ul-Qurun, (the best of all the times, or the best period of the Ummah).