The Prophet (saas) was a bearer of glad tidings

In the verse "O Prophet! We have sent you as a witness, and a bringer of good news and a warner" (Surat al-Ahzab: 45), Allah describes the Prophet (saas) as a bearer of glad tidings and a warner. The Prophet (saas) always warned people against the sufferings to be experienced in Hell, and told them of the desirable future that awaited the good in this world, and of the infinite life of the Paradise in the hereafter. Allah reveales this characteristic of the Prophet (saas) in the Qur'an thus:

We have sent you with the Truth, bringing good news and giving warning. Do not ask about the inhabitants of the Blazing Fire. (Surat al-Baqara: 119)

We have sent it down with truth and with truth it has come down. We only sent you to bring good news and to give warning. (Surat al-Isra': 105)

We only sent you for the whole of mankind, bringing good news and giving warning. But most of mankind do not know it. (Surah Saba': 28)

Those who take the Prophet (saas) as a model and abide by his Sunnah must, like him, give people the same glad tidings and warn them. The Prophet (saas) himself described how such people ought to behave:

"Make things easy for the people, and do not make it difficult for them, and make them calm (with glad tidings) and do not repulse (them)." 

Giving welcome news increases believers' enthusiasm and morale, and encourages them to be more determined and persevering in their labors in the way of Allah. Someone who hopes to be rewarded with Paradise will of course have a very different attitude and state of mind than someone who regards those labors as monotonous, or carries them out of habit or a sense of obligation. That is why Allah has commanded His Messenger (saas) to: "Spur on the believers." (Surat an-Nisa': 84)

In another verse, Allah says: "Give good news to the believers that they will receive immense favor from Allah" (Surat al-Ahzab: 47). Every believer who abides by Allah's commandments and the morality of the Prophet (saas) is responsible for giving good news to Muslims, and for encouraging them. It is not proper for a Muslim to speak in a manner that is negative, to make easy tasks appear difficult, and thus, to discourage the faithful, to forget the beautiful things and good news Allah has revealed in the Qur'an, thereby leading the faithful to become pessimistic. What is in conformity with the Qur'an is, like the manner of the Prophet (saas), to recall the good things promised to the faithful by Allah, and to keep to revitalize them.

One such tidings the Prophet (saas) was told to tell people about was Allah's forgiveness of sins:

Say: "My servants, you who have transgressed against yourselves, do not despair of the mercy of Allah. Truly Allah forgives all wrong actions. He is the Ever-Forgiving, the Most Merciful." (Surat az-Zumar: 53)

When those who believe in Our Signs come to you, say, "Peace be upon you!" Allah has made mercy incumbent on Himself. If anyone among you does evil out of ignorance and then afterwards repents and puts things right, He is Ever-Forgiving, Most Merciful. (Surat al-An‘am: 54)

Another tiding is that of Paradise:

Say, "Shall I tell you of something better than that?" Those who do their duty will have Gardens with their Lord, with rivers flowing under them, remaining in them timelessly, for ever, and purified wives, and the Pleasure of Allah. Allah sees His servants. (Surah Al ‘Imran: 15)

(For further reading about the attributes of the Prophet(saas), see “The Prophet Muhammad (saas)” by Harun Yahya)