To answer your question, I'm just going to copy paste from ibn kathir's tafsir:
Islam Has Been Perfected For Muslims
Allah said,
[الْيَوْمَ أَكْمَلْتُ لَكُمْ دِينَكُمْ وَأَتْمَمْتُ عَلَيْكُمْ نِعْمَتِى وَرَضِيتُ لَكُمُ الأِسْلاَمَ دِيناً]
(This day, I have perfected your religion for you, completed My favor upon you, and have chosen for you Islam as your religion.) This, indeed, is the biggest favor from Allah to this Ummah, for He has completed their religion for them, and they, thus, do not need any other religion or any other Prophet except Muhammad . This is why Allah made Muhammad the Final Prophet and sent him to all humans and Jinn. Therefore, the permissible is what he allows, the impermissible is what he prohibits, the Law is what he legislates and everything that he conveys is true and authentic and does not contain lies or contradictions. Allah said;
[وَتَمَّتْ كَلِمَةُ رَبِّكَ صِدْقاً وَعَدْلاً]
(And the Word of your Lord has been fulfilled in truth and in justice,) meaning, it is true in what it conveys and just in what it commands and forbids. When Allah completed the religion for Muslims, His favor became complete for them as well. Allah said,
[الْيَوْمَ أَكْمَلْتُ لَكُمْ دِينَكُمْ وَأَتْمَمْتُ عَلَيْكُمْ نِعْمَتِى وَرَضِيتُ لَكُمُ الأِسْلاَمَ دِيناً]
(This day, I have perfected your religion for you, completed My favor upon you, and have chosen for you Islam as your religion.) meaning, accept Islam for yourselves, for it is the religion that Allah likes and which He chose for you, and it is that with which He sent the best of the honorable Messengers and the most glorious of His Books. Ibn Jarir recorded that Harun bin `Antarah said that his father said, "When the Ayah,
[الْيَوْمَ أَكْمَلْتُ لَكُمْ دِينَكُمْ]
(This day, I have perfected your religion for you...) was revealed, during the great day of Hajj (the Day of `Arafah, the ninth day of Dhul-Hijjah) `Umar cried. The Prophet said, `What makes you cry' He said, `What made me cry is that our religion is being perfected for us. Now it is perfect, nothing is perfect, but it is bound to deteriorate.' The Prophet said,
«صَدَقْت»
(You have said the truth.)'' What supports the meaning of this Hadith is the authentic Hadith,
«إِنَّ الْإِسْلَامَ بَدَأَ غَرِيبًا، وَسَيَعُودُ غَرِيبًا، فَطُوبَى لِلْغُرَبَاء»
(Islam was strange in its beginning and will return strange once more. Therefore, Tuba for the strangers.) Imam Ahmad recorded that Tariq bin Shihab said, "A Jewish man said to `Umar bin Al-Khattab, `O Leader of the Believers! There is a verse in your Book, which is read by all of you (Muslims), and had it been revealed to us, we would have taken that day (on which it was revealed) as a day of celebration.' `Umar bin Al-Khattab asked, `Which is that verse' The Jew replied, s
[الْيَوْمَ أَكْمَلْتُ لَكُمْ دِينَكُمْ وَأَتْمَمْتُ عَلَيْكُمْ نِعْمَتِى]
(This day, I have perfected your religion for you, completed My favor upon you...) `Umar replied, `By Allah! I know when and where this verse was revealed to Allah's Messenger . It was the evening on the Day of `Arafah on a Friday.''' Al-Bukhari recorded this Hadith through Al-Hasan bin As-Sabbah from Ja`far bin `Awn. Muslim, At-Tirmidhi and An-Nasa'i also recorded this Hadith. In the narration collected by Al-Bukhari in the book of Tafsir, through Tariq, he said, "The Jews said to `Umar, `By Allah! There is a verse that is read by all of you (Muslims), and had it been revealed to us, we would have taken that day (on which it was revealed) as a day of celebration.' `Umar said, `By Allah! I know when and where this verse was revealed and where the Messenger of Allah was at that time. It was the day of `Arafah, and I was at `Arafah, by Allah.'' Sufyan (one of the narrators) doubted if Friday was mentioned in this narration. Sufyan's confusion was either because he was unsure if his teacher included this statement in the Hadith or not. Otherwise, if it was because he doubted that the particular day during the Farewell Hajj was a Friday, it would be a mistake that could not and should not have come from someone like Sufyan Ath-Thawri. The fact that it was a Friday, is agreed on by the scholars of Sirah and Fiqh. There are numerous Hadiths that support this fact that are definitely authentic and of the Mutawatir type. This Hadith was also reported from `Umar through various chains of narration.
I hope that answers your question :)