Muhammad's Prophecy is a Great Bounty from Allah
Allah says;
كَمَا أَرْسَلْنَا فِيكُمْ رَسُولاً مِّنكُمْ يَتْلُو عَلَيْكُمْ ايَاتِنَا وَيُزَكِّيكُمْ وَيُعَلِّمُكُمُ الْكِتَابَ وَالْحِكْمَةَ وَيُعَلِّمُكُم مَّا لَمْ تَكُونُواْ تَعْلَمُونَ
Similarly (to complete My blessings on you), We have sent among you a Messenger (Muhammad) of your own, reciting to you Our verses (the Qur'an) and purifying you, and teaching you the Book (the Qur'an) and the Hikmah (i.e., Sunnah, Islamic laws and Fiqh ـ jurisprudence), and teaching you that which you did not know.
Allah reminds His believing servants with what He has endowed them with by sending Muhammad as a Messenger to them, reciting to them Allah's clear Ayat and purifying and cleansing them from the worst types of behavior, the ills of the souls and the acts of Jahiliyyah (pre-Islamic era). The Messenger also takes them away from the darkness (of disbelief) to the light (of faith) and teaches them the Book, the Qur'an, and the Hikmah (i.e., the wisdom), which is his Sunnah. He also teaches them what they knew not.
During the time of Jahiliyyah, they used to utter foolish statements. Later on, and with the blessing of the Prophet's Message and the goodness of his prophecy, they were elevated to the status of the Awliya (loyal friends of Allah) and the rank of the scholars. Hence, they acquired the deepest knowledge among the people, the most pious hearts, and the most truthful tongues.
Allah said;
لَقَدْ مَنَّ اللَّهُ عَلَى الْمُومِنِينَ إِذْ بَعَثَ فِيهِمْ رَسُولاً مِّنْ أَنفُسِهِمْ يَتْلُواْ عَلَيْهِمْ ءَايَـتِهِ وَيُزَكِّيهِمْ
Indeed, Allah conferred a great favor on the believers when He sent among them a Messenger (Muhammad) from among themselves, reciting unto them His verses (the Qur'an), and purifying them (from sins). (3;164)
Allah also criticized those who did not give this bounty its due consideration, when He said;
أَلَمْ تَرَ إِلَى الَّذِينَ بَدَّلُواْ نِعْمَتَ اللَّهِ كُفْرًا وَأَحَلُّواْ قَوْمَهُمْ دَارَ الْبَوَارِ
Have you not seen those who have changed the favors of Allah into disbelief (by denying Prophet Muhammad) and his Message of Islam), and caused their people to dwell in the house of destruction. (14;28)
Ibn Abbas commented,
"Allah's favor means Muhammad."
Therefore, Allah has commanded the believers to affirm this favor and to appreciate it by thanking and remembering Him;
فَاذْكُرُونِي أَذْكُرْكُمْ وَاشْكُرُواْ لِي وَلَا تَكْفُرُونِ