Allah said:
﴿وَكَذَلِكَ جَعَلْنَـكُمْ أُمَّةً وَسَطًا لِّتَكُونُواْ شُهَدَآءَ عَلَى النَّاسِ وَيَكُونَ الرَّسُولُ عَلَيْكُمْ شَهِيدًا﴾
(Thus We have made you ﴿true Muslims﴾, a Wasat (just) (and the best) nation, that you be witnesses over mankind and the Messenger (Muhammad ) be a witness over you.)
Allah stated that He has changed our Qiblah to the Qiblah of Ibrahim and chose it for us so that He makes us the best nation ever. Hence, we will be the witnesses over the nations on the Day of Resurrection, for all of them will then agree concerning our virtue. The word Wasat in the Ayah means the best and the most honored. Therefore, saying that (the Prophet's tribe) Quraysh is in the Wasat regarding Arab tribes and their areas, means the best. Similarly, saying that Allah's Messenger was in the Wasat of his people, means he was from the best subtribe. Also, `Asr, the prayer that is described as `Wusta' (a variation of the word Wasat), means the best prayer, as the authentic collections of Ahadith reported. Since Allah made this Ummah (Muslim nation) the Wasat, He has endowed her with the most complete legislation, the best Manhaj (way, method, etc.,) and the clearest Madhhab (methodology, mannerism, etc). Allah said:
﴿هُوَ اجْتَبَـكُمْ وَمَا جَعَلَ عَلَيْكمْ فِى الدِّينِ مِنْ حَرَجٍ مِّلَّةَ أَبِيكُمْ إِبْرَهِيمَ هُوَ سَمَّـكُمُ الْمُسْلِمِينَ مِن قَبْلُ وَفِى هَـذَا لِيَكُونَ الرَّسُولُ شَهِيداً عَلَيْكُمْ وَتَكُونُواْ شُهَدَآءَ عَلَى النَّاسِ﴾
(He has chosen you (to convey His Message of Islamic Monotheism to mankind), and has not laid upon you in religion any hardship: it is the religion of your father Ibrahim. It is He (Allah) Who has named you Muslims both before and in this (the Qur'an), that the Messenger (Muhammad ) may be a witness over you and you be witnesses over mankind!) (22:78)
Moreover, Imam Ahmad reported that Abu Sa`id narrated: Allah's Messenger said:
«يُدْعَى نُوحٌ يَوْمَ الْقِيَامة، فَيُقَالُ لَهُ: هَلْ بَلَّغْتَ؟ فَيَقُولُ: نَعَمْ، فَيُدْعَى قَوْمُهُ فَيُقَالُ لَهُمْ: هَلْ بَلَّغَكُمْ فَيَقُولُونَ: مَا أتَانَا مِنْ نَذِيرٍ وَمَا أتَانَا مِنْ أَحَدٍ، فَيُقَالُ لِنُوح: مَنْ يَشْهَدُ لَكَ؟ فَيَقُولُ: مُحَمَّدٌ وَأُمَّتُهُ، قال فَذلِكَ قَوْلُهُ:
﴿وَكَذَلِكَ جَعَلْنَـكُمْ أُمَّةً وَسَطًا﴾
قَالَ: والْوَسَطُ الْعَدْلُ، فَتُدْعَون فَتَشْهَدُونَ لَهُ بِالْبَلَاغِ ثُمَّ أَشْهَدُ عَلَيْكُم»
(Nuh will be called on the Day of Resurrection and will be asked, `Have you conveyed (the Message)' He will say, `Yes.' His people will be summoned and asked, `Has Nuh conveyed (the Message) to you' They will say, `No warner came to us and no one (Prophet) was sent to us.' Nuh will be asked, `Who testifies for you' He will say, `Muhammad and his Ummah.')
This is why Allah said:
﴿وَكَذَلِكَ جَعَلْنَـكُمْ أُمَّةً وَسَطًا﴾
(Thus We have made you a Wasat nation.)
The Prophet said; (The Wasat means the `Adl (just). You will be summoned to testify that Nuh has conveyed (his Message), and I will attest to your testimony.)
It was also recorded by Al-Bukhari, At-Tirmidhi, An-Nasa'i and Ibn Majah.
Imam Ahmad also reported that Abu Sa`id Khudri narrated: Allah's Messenger said:
«يَجِيءُ النَّبِيُّ يَوْمَ الْقِيَامَةِ وَمَعَهُ الرَّجُلَانِ وَأَكْثَرُ مِنْ ذلِكَ، فيُدْعَى قَوْمُهُ، فَيُقَالُ: هَلْ بَلَّغَكُمْ هَذَا؟ فَيَقُولُونَ: لَا فَيُقالُ لَهُ: هَلْ بَلَّغْتَ قَوْمَكَ؟ فَيَقُولُ: نَعَمْ، فَيُقالُ: مَنْ يَشْهَدُ لَكَ؟ فَيَقُولُ: مُحَمَّدٌ وَأُمَّتُهُ، فَيُدْعَى مُحَمَّدٌ وَأُمَّتُهُ، فَيُقَالُ لَهُمْ: هَلْ بَلَّغَ هذَا قَوْمَهُ؟ فَيَقُولُونَ: نَعَمْ، فَيُقَالُ: وَمَا عِلْمُكُمْ؟ فَيَقُولُونَ: جَاءَنَا نَبِيُّنَاصلى الله عليه وسلّم فأخْبَرَنَا أَنَّ الرُّسُلَ قَدْ بَلَّغُوا، فَذلِك قَوْلُهُ عَزَّ وَجَلَّ:
﴿وَكَذَلِكَ جَعَلْنَـكُمْ أُمَّةً وَسَطًا﴾
قَالَ: عَدْلًا
﴿وَكَذَلِكَ جَعَلْنَـكُمْ أُمَّةً وَسَطًا لِّتَكُونُواْ شُهَدَآءَ عَلَى النَّاسِ وَيَكُونَ الرَّسُولُ عَلَيْكُمْ شَهِيدًا﴾
(The Prophet would come on the Day of Resurrection with two or more people (his only following!), and his people would also be summoned and asked, `Has he (their Prophet) conveyed (the Message) to you' They would say, `No.' He would be asked, `Have you conveyed (the Message) to your people' He would say, `Yes.' He would be asked, `Who testifies for you' He would say, `Muhammad and his Ummah.' Muhammad and his Ummah would then be summoned and asked, `Has he conveyed (the Message) to his people' They would say, `Yes.' They would be asked, `Who told you that' They would say, `Our Prophet (Muhammad) came to us and told us that the Messengers have conveyed (their Messages). ')
Hence Allah's statement:
﴿وَكَذَلِكَ جَعَلْنَـكُمْ أُمَّةً وَسَطًا﴾
(Thus We have made you a Wasat nation.)
He said, "(meaning) the `Adl,' (he then continued reciting the Ayah):
﴿وَكَذَلِكَ جَعَلْنَـكُمْ أُمَّةً وَسَطًا لِّتَكُونُواْ شُهَدَآءَ عَلَى النَّاسِ وَيَكُونَ الرَّسُولُ عَلَيْكُمْ شَهِيدًا﴾
(Thus We have made you, a just (and the best) nation, that you be witnesses over mankind and the Messenger (Muhammad ) be a witness over you.)''
Furthermore, Imam Ahmad reported that Abul-Aswad narrated: I came to Al-Madinah and found that an epidemic had broken out that caused many fatalities. I sat next to `Umar bin Al-Khattab once when a funeral procession started and the people praised the dead person. `Umar said, "Wajabat (it will be recorded as such), Wajabat!'' Then another funeral was brought forth and the people criticized the dead person. Again, `Umar said, "Wajabat.'' Abul-Aswad asked, "What is Wajabat, O Leader of the faithful'' He said, "I said just like Allah's Messenger had said:
«أَيُّمَا مُسْلِمٍ شَهِدَ لَهُ أَرْبَعَةٌ بِخَيْر أَدْخَلَهُ اللهُ الْجَنَّــة»
قَالَ: فَقُلْنَا وَثَلَاثَةٌ؟ قَالَ: فَقَالَ:
«وَثَلَاثَــــة»
قَالَ: فَقُلْنَا وَاثْنَانِ: قَالَ
«وَاثْنَان»
. ثُمَّ لَمْ نَسْأَلْهُ عَنِ الْوَاحِدِ.
(Any Muslim for whom four testify that he was righteous, then Allah will enter him into Paradise.' We said, `What about three' He said, `And three.' We said, `And two' He said, `And two.' We did not ask him about (the testimony) of one (believing) person.)''
This was also recorded by Al-Bukhari, At-Tirmidhi, and An-Nasa'i.