Surah al-Tawbah: (3) "And a proclamation from Allah..."
{And a proclamation}: Its nominative case is like the nominative case of Bara'ah (Disavowal) in both possible interpretations. The sentence is then conjoined to its counterpart. There is no basis for the claim of those who say it is conjoined to Bara'ah, just as one does not say "Amr is conjoined to Zayd" in your saying: "Zayd is standing, and Amr is sitting."
Al-Adhan (proclamation) is in the sense of al-idhan (informing), just as al-aman (security) and al-'ata' (giving) are in the sense of al-iman (believing) and al-i'ta' (giving).
If you ask: What is the difference between the meaning of the first sentence and the second?
I say: The first is an announcement of the establishment of the disavowal, while this is an announcement of the obligation to inform [people] of what has been established.
If you ask: Why was the disavowal linked to those of the polytheists with whom you had a treaty, while the proclamation was linked to "the people"?
I say: Because the disavowal is specific to those who had treaties and those who broke them, whereas the proclamation is general for all people—those who had a treaty and those who did not, and those among the treaty-holders who broke it and those who did not.
{The day of the Greater Hajj}: The Day of Arafah. It is also said: The Day of Sacrifice (Yawm al-Nahr), because the completion of the Hajj and the majority of its acts—such as the circumambulation (tawaf), the sacrifice, the shaving of the head, and the stoning—occur on it.
It is narrated from Ali (may Allah be pleased with him) that a man took hold of his mount’s bridle and asked, "What is the Greater Hajj?" He replied, "This day of yours. Let go of my mount."
From Ibn Umar (may Allah be pleased with them both): The Messenger of Allah (peace be upon him) stood on the Day of Sacrifice at the Jamarat during the Farewell Pilgrimage and said, "This is the day of the Greater Hajj."
Hajj is described as "greater" because the Umrah is called the "Lesser Hajj." Alternatively, the standing at Arafah is considered the Greater Hajj because it is the most important of its obligations; if it is missed, the Hajj is missed. Likewise, if the Day of Sacrifice is intended, it is because the majority of the acts of Hajj are performed on it, thus it is the Greater Hajj.
From al-Hasan (may Allah be pleased with him): It was called the day of the Greater Hajj because of the gathering of Muslims and polytheists on that day, and its coincidence with the festivals of the People of the Book—a convergence that did not happen before or after it—so it was magnified in the heart of every believer and disbeliever.
The ba' (preposition), which is the connector for al-adhan, has been omitted for brevity. It is recited as inna Allaha (with a kasra) because al-adhan carries the meaning of a statement.
{And His Messenger}: Conjoined to the implied subject in bari'un (disavowed), or to the position of inna and its noun. It is also recited in the accusative case, as a conjunction to the noun of inna, or because the waw is in the sense of "with" (i.e., He is disavowed, along with His Messenger, from them). It is also recited in the genitive case due to proximity (jiwar), or as an oath, like his saying: "By your life (la-'amruka)."
It is told that a Bedouin heard a man recite it [incorrectly], so he said, "If Allah is disavowed from His Messenger, then I am disavowed from Him!" The man grabbed him by his garment and took him to Umar, and the Bedouin recounted his recitation. It was then that Umar (may Allah be pleased with him) ordered the learning of Arabic.
{So if you repent}: From disbelief and treachery, {it is better for you; but if you turn away}: From repentance, or if you persist in turning away and shunning Islam and faithfulness, {then know that you will not cause failure to Allah}: You will not escape His power, nor will you evade His seizure and punishment.
{Except for those with whom you made a treaty among the polytheists and who have not been deficient toward you in anything or supported anyone against you; so complete for them their treaty until their term [has ended]. Indeed, Allah loves the righteous.}