Answer: It means that Allah sent him to the worlds as a bringer of glad tidings and as a warner.

It is a must to:

1. Obey his commands

2. Believe his reports

3. Refrain from disobeying him

4. Worship Allah only in compliance with his Sharia, which requires following the Sunnah and abandoning religious innovations.

Allah Almighty says: {Whoever obeys the Messenger has indeed obeyed Allah.} [Surat an-Nisā’: 80] He also says: {Nor does he speak out of his own desire. It is but a revelation sent down [to him].} [Surat an-Najm: 3-4] Allah Almighty also says: {Indeed, in the Messenger of Allah you have an excellent example for those who look forward to Allah and the Last Day, and remember Allah much.} [Surat al-Ahzāb: 21]