[Surah Al-Qalam 68:4]
Abdullah ibn Amr bin Al-As (May Allah be pleased with him) once presented a verse from the books of Ahlul kitab which mentions 16 attributes of the Prophet ﷺ. Three of them are similar to Qur'anic ayat of Surah Al-Fath:
"O Prophet we have sent you as a witness"Surah Al-Fath
Like every Prophet, Muhammad ﷺ is also a witness upon his people and a caretaker, and he will be questioned about his duty on the Day of Judgement.
The second context is explained in the Qur'an; He will be a witness for all Prophets and their people who were sent before him.
On the Day of Judgement when Nuh (peace be upon him) will be asked, "Did you convey My message to the people?" He will reply in affirmation. Then Allah ﷻ will ask his people if they got the Message from their Prophet Nuh, who would deny it . Allah ﷻ would ask Nuh to provide evidence for his claim, even though He is aware of the truth. Nuh will then say that The Prophet Muhammad ﷺ and his ummah are his witness. So Allah ﷻ will call upon Prophet Muhammad ﷺ who would testify in favour of Nuh (peace be upon him). Allah ﷻ will ask his ummah:
You were not present then, how did you know?
Prophet Muhammad's ﷺ ummah will reply: We had read it in our Qur’an.
This testimony by the followers of Islam will be given for all the Prophets.
Mubashir - A Giver of glad tidings - Mubashir (Bashirun) means one who gives surety (safety) and glad tidings as the Qur’an says:
Wa Bashhiril Mo’mineen -
and give glad tidings to the Believers
In order to motivate the Muslims to acquire the best Akhlaq (character), Allah ﷻ informed them about the virtues of charity and how it would be helpful to the donor even after he dies. His glad tidings motivate the people to help the needy. Thus, it is an excellent characteristic to encourage others to do good.
Naziran -A Warner - The term ‘Nazir’ means one who gives a warning of severe punishments for those who commit sins and reject the commands of Allah ﷻ and His Messenger ﷺ . It is a part of good character to caution people against harm, loss or danger. For example, you notice a pit on the road during heavy rainfall.. A man drives by in his car and is going towards the pit. Your good character would stop the man from going towards the pit which can otherwise be harmful to him.
The three noble characteristics of the Prophet ﷺ mentioned above were also mentioned in Torah and Injeel.