Tafsir of Al-Ma'idah 5:51

Ibn Jarir and Ibn Abi Hatim narrated from al-Suddi, who said: "When the Battle of Uhud occurred, it became severe for a group of people, and they feared that the disbelievers would gain the upper hand over them. One man said to his companion, 'As for me, I will join such-and-such Jew and take a guarantee of safety from him, and I will become a Jew with him, for I fear that the Jews may prevail over us.' The other said, 'As for me, I will join such-and-such Christian in some land of the Levant and take a guarantee of safety from him, and I will become a Christian with him.' Then God, the Almighty, revealed concerning them, forbidding them: 'O you who have believed,' etc."

Ibn Jarir and Ibn Abi Shaybah narrated from Atiyyah ibn Sa’d, who said: "Ubadah ibn al-Samit from the Banu al-Harith ibn al-Khazraj came to the Messenger of God (may God bless him and grant him peace) and said, 'O Messenger of God, I have many allies among the Jews, and I declare to God, the Almighty, and His Messenger (may God bless him and grant him peace) my disavowal of the alliance of the Jews, and I take God, the Almighty, and His Messenger as my allies.' Abdullah ibn Ubayy said, 'I am a man who fears the turns of fortune; I will not disavow the alliance of my protégés.' Then was revealed: 'Some of them are allies of others.' That is, some Jews are allies to some of them, and some Christians are allies to some of them. Generalization was preferred because the intent is clear, for it is evident that Jews do not ally themselves with Christians, and vice versa. The sentence is a new start (istinaf), providing a rationale for the preceding prohibition and emphasizing the obligation to avoid what was forbidden. That is: Some of them are allies to others, in agreement on one word in everything they do and refrain from, and a necessity of that is the unanimity of all of them in opposing and harming you, to the point that they inflict evil upon you and desire calamities for you. How, then, is an alliance between you and them conceivable?"

Al-Hawfi claimed that the sentence occupies the position of an adjective for "allies," but the apparent meaning is the first.

His saying, Exalted is He: "And whoever among you takes them as an ally, then he is one of them," meaning, he is of their group, and his ruling is their ruling. This is like a conclusion drawn from what preceded it, and it is framed in a way that emphasizes and maximizes the deterrent, for if the one who takes them as an ally were truly one of them [in faith], he would be a disbeliever, and that is not the intended meaning. It is said: The intent is, "Whoever among you takes them as an ally is a disbeliever like them in reality," and this is narrated from Ibn Abbas—may God be pleased with them both—and perhaps that is when their taking them as allies is due to them being Jews or Christians. It is also said: Rather, it is because the verse was revealed concerning the hypocrites, and the meaning is that by this alliance, they become manifest disbelievers.

His saying, Exalted is He: "Indeed, God does not guide the wrongdoing people,"—whether they wrong themselves by befriending the disbelievers, or wrong the believers by befriending their enemies—is another rationale, as has been said, which includes the fact that there is no benefit in befriending the disbelievers; rather, harm results from it. It is also said: It is a rationale for why the one who takes them as an ally is one of them; meaning, He does not guide them to faith, but leaves them to their own devices, so they fall into disbelief and misguidance. The explicit noun was placed in the position of the pronoun as a warning that taking them as an ally is an act of wrongdoing, because it exposes the soul to eternal punishment and is a placement of something in other than its proper place.