Al-Baqarah: 136–137
"Say: We believe in Allah..."
"Say"
An address to the believers. It is also permissible that it is an address to the disbelievers, meaning: "Say this so that you may be upon the truth; otherwise, you are upon falsehood."
"Nay, the creed of Abraham"
It is permissible that this implies: "Nay, follow you the creed of Abraham," or "Be you the people of his creed."
"The Sibt (grandson)"
The Sibt is the grandson. Al-Hasan and Al-Husayn were the two sibts of the Messenger of Allah (ﷺ).
"And the Asbat (descendants)"
The grandsons of Jacob, the offspring of his twelve sons.
"We make no distinction between any of them"
We do not believe in some and disbelieve in others, as the Jews and Christians have done.
"Any" (ahad)
It carries the meaning of a collective group, which is why it is grammatically correct for "between" (bayna) to precede it.
"With the like of what you believe in"
This is by way of rebuke (tabkit), for the religion of truth is one and has no equal; it is the religion of Islam. "And whoever seeks a religion other than Islam, it will never be accepted from him" (Al Imran: 85). Therefore, there exists no other religion that equals the religion of Islam in being the truth, such that if they believed in that "equal" religion, they would be guided. Thus, it is said: "If they believe..." using the conditional particle of doubt for the sake of hypothesis and supposition. It means: "If they were to obtain another religion like yours, equal to it in correctness and soundness, then they would be guided."
This implies that the religion they are upon, and every religion other than it, is divergent and not equal to it, because it is truth and guidance, while all else is falsehood and misguidance.
This is similar to your saying to a man you are advising: "This is the correct opinion; if you have an opinion more correct than it, then act upon it," while you know full well there is no opinion more correct than yours. You only intend to rebuke your companion and make him realize that there is no opinion beyond what you have seen.
It is also possible that the ba (in bi-mithli) is not a connective particle, but rather the ba of instrumentality (isti'ana), like saying "I wrote with the pen" or "I worked with the adze." It would mean: "If they enter into faith by means of a testimony like the testimony you have believed in."
Ibn Abbas and Ibn Mas'ud read it as: bima amantum bihi (with what you believe in). Ubayy read it as: billadhi amantum bihi (with that which you believe in).
"But if they turn away"
From what you say to them and refuse to be fair, they are nothing but:
"In opposition"
Meaning: in hostility and stubbornness, nothing else. They have no part in the pursuit of truth. Or, it means: if they turn away from the testimony and from entering into faith through it.
"Allah will suffice you against them"
A guarantee from Allah to grant His Messenger (ﷺ) victory over them. He fulfilled His promise by the killing and enslavement of [Banu] Qurayza and the expulsion of Banu al-Nadir. The sin (in sa-yakfikahum) signifies that this will inevitably come to pass, even if it is delayed for a time.
"And He is the All-Hearing, the All-Knowing"
A threat to them: He hears what they utter and knows the envy and malice they conceal, and He will punish them for it. Or, it is a promise to the Messenger of Allah (ﷺ), meaning: He hears what you pray for and knows your intention and what you desire regarding the manifestation of the religion of truth; He will answer you and bring you to your goal.