Tafsir of Al Imran 3:149

This is the commencement of a rebuke directed at the believers, dissuading them from following the disbelievers by explaining the harms thereof, immediately following the encouragement to emulate the supporters of the prophets, upon them be peace, by illustrating their virtues. The address is initiated with a call and an alerting to demonstrate the importance of what is contained therein, and they are described with faith to remind them of a state that contradicts such obedience, thereby rendering the rebuke most perfect.

As for "those who have disbelieved," it refers either to:

1. The Hypocrites: Since the verse was revealed, as narrated from Ali—may Allah, the Most High, ennoble his countenance—when they said to the believers at the time of the defeat: "Return to your brothers and enter into their religion." The expression of them in this manner is intended to increase aversion toward them and caution against obeying them.
2. Abu Sufyan and his companions: In this case, obedience to them refers to submission and seeking safety from them; this is the view of al-Suddi.
3. The Jews and the Christians: In this case, it means: "Do not accept advice from the Jews and the Christians regarding your religion, and do not believe them in anything related to it." This is the view of Ibn Jurayj, who related that they used to cast doubts upon them regarding the religion, saying: "If Muhammad—may Allah, the Most High, grant him peace—were a true prophet, he would not have been defeated, nor would what befell him and his companions have occurred. He is merely a man whose situation is like the situation of others among people; one day for him and one day against him." Thus, they were forbidden from paying heed to these claims.
4. All other disbelievers.

Some later scholars have held that this is permissible, and have asserted that the use of "if" (in) is to signify that such obedience is unlikely to occur on the part of the believers.

"They will turn you back on your heels": That is, they will return you to your initial state, which is polytheism toward Allah, the Most High. The verb is the response to the conditional clause.

This is considered valid based on the narration from Ali—may Allah, the Most High, ennoble his countenance—even though the discourse, in its essence, carries the strength of: "If you obey those who have disbelieved" in their saying: "Return to your brothers and enter into their religion," [it is as if it says] "they will cause you to enter their religion." It leads to the meaning: "If you enter their religion, you enter their religion," which involves the unification of the condition and the response. This is based on the premise that "turning back on one's heels" is an idiom for the reversal of affairs and an allegory for decline after advancement.

It has been said: The intended meaning of obedience is the resolve to do so and the determination upon it; that is, "If you are determined to obey them in that, you will be turned back and return to the state of disbelief you were once in." This is more eloquent in terms of rebuke, though it is distant from the literal wording. It is also permitted that the response to the condition is considered in light of it being a preamble to the words of the Almighty: "And you will turn back as losers"—that is, you will return having lost the good of this world and the felicity of the Hereafter, and that is the greatest loss.