Al-Baqarah: 217
"They ask you about the sacred month..."
The Messenger of Allah (ﷺ) dispatched Abdullah ibn Jahsh on a military expedition in Jumada al-Akhirah, two months before the Battle of Badr, to monitor a Quraysh caravan. In it was Amr ibn Abdullah al-Hadrami and three others. They killed him, captured two, and seized the caravan, which contained trade goods from Ta'if. This occurred on the first day of Rajab, though they had mistaken it for Jumada al-Akhirah.
Quraysh said: "Muhammad has made the sacred month lawful—a month in which the fearful are safe and people scatter to their livelihoods." The Messenger of Allah (ﷺ) detained the caravan, and the members of the expedition were deeply distressed, saying, "We will not depart until our repentance is revealed." The Messenger of Allah (ﷺ) returned the caravan and the captives.
From Ibn Abbas (may Allah be pleased with him): When this was revealed, the Messenger of Allah (ﷺ) took the spoils. The meaning is: The disbelievers or the Muslims ask you about fighting in the sacred month.
"Fighting in it" is a badal ishtimal (substitution of inclusion) for "the sacred month." In the recitation of Abdullah, it is "about fighting in it," repeating the governing agent, similar to His saying: "For the oppressed, for those who believe among them" (An-Nisa: 75). Ikrimah recited: "Killing in it—say, 'Killing in it is a great [sin].'" Meaning: a great sin.
Ata was asked about fighting in the sacred month, and he swore by Allah that it is not lawful for people to raid in the Sacred Precinct nor in the sacred month, unless they are fought therein, and that it has not been abrogated. However, most opinions hold that it is abrogated by His saying: "Kill the polytheists wherever you find them" (At-Tawbah: 5).
"And averting [people] from the way of Allah" is a subject, and "greater" is its predicate. It means: The great sins of Quraysh—their averting people from the way of Allah, from the Sacred Mosque, their disbelief in Allah, and their expulsion of the people of the Sacred Mosque (the Messenger and the believers)—are "greater in the sight of Allah" than what the expedition did by fighting in the sacred month, which was done by mistake and based on conjecture.
"And fitnah" refers to expulsion or polytheism. "The Sacred Mosque" is conjoined to "the way of Allah"; it is not permissible to conjoin it to the pronoun in "in it" (bihi).
"And they will continue to fight you" is an announcement of the permanence of the disbelievers' enmity toward the Muslims, and that they will not cease until they turn them back from their religion. "Until" here implies causality, like saying: "So-and-so worships Allah until he enters Paradise," meaning: they fight you in order to turn you back.
"If they are able" expresses the impossibility of their ability, like a man saying to his enemy, "If you overcome me, do not spare me," while being confident that he will not be overcome.
"And whoever of you reverts"—whoever turns back from his religion to theirs and obeys them in reverting to it.
"And dies" while in a state of apostasy, "for those, their deeds have become worthless in this world and the Hereafter." This is due to what they lose by the act of apostasy—the fruits of Islam that Muslims enjoy in this world—and by persisting in it and dying upon it, the reward of the Hereafter. Al-Shafi'i used this as evidence that apostasy does not nullify deeds until one dies upon it. According to Abu Hanifah, it nullifies them even if one returns to Islam.
"Indeed, those who have believed and those who have emigrated..."
It is narrated that when Abdullah ibn Jahsh and his companions killed al-Hadrami, some people thought that even if they were safe from sin, they had no reward. Thus, "Those hope for the mercy of Allah" was revealed. Qatadah said: These are the best of this nation. Allah then made them people of hope, as you hear. Whoever hopes, seeks; and whoever fears, flees.