His saying, “So fear Allah and set right what is between you,” means: Fear Allah by obeying Him, and reconcile matters among yourselves by abandoning dispute and discord, and by entrusting the matter of the spoils to Allah and the Messenger, peace and blessings be upon him. “And obey Allah and His Messenger, if you are believers.”
“Indeed, the believers are only those who, when Allah is mentioned, their hearts tremble; and when His verses are recited to them, they increase them in faith; and upon their Lord they rely (2)—those who establish prayer and spend from what We have provided them (3)—those are the true believers. For them are degrees with their Lord, forgiveness, and a noble provision (4).”
“Indeed, the believers are only”—that is, the believer is not one who disobeys Allah and His Messenger. Rather, the believers are those who are sincere in their faith: “those who, when Allah is mentioned, their hearts tremble”—their hearts fear and are filled with awe. It was also said: when they are admonished through Allah, they submit out of fear of His punishment. “And when His verses are recited to them, they increase them in faith”—in affirmation and certainty.
Umayr ibn Habib, who was a Companion, said: “Faith increases and decreases.” He was asked, “What is its increase?” He replied, “When we remember Allah and praise Him, that is its increase; and when we become heedless and inattentive, that is its decrease.” Umar ibn Abd al-Aziz wrote to Adi ibn Adi: “Faith has obligatory duties, conditions, prescribed laws, limits, and sunnahs. Whoever fulfils them has perfected faith, and whoever does not fulfil them has not perfected faith.”
“And upon their Lord they rely”—that is, they entrust their affairs to Him, place their trust in Him, hope in no one besides Him, and fear none other than Him.
“Those are the true believers,” meaning: certainly. Ibn Abbas said: “They are free from disbelief.” Muqatil said: “Truly—they are believers whose faith is beyond doubt.” This indicates that not everyone may describe himself as being a true believer, for Allah, Exalted is He, described only particular people in this way, possessing particular qualities; and no one can be certain that these qualities are present in himself.
Ibn Abi Najih said: A man asked al-Hasan, “Are you a believer?” He replied, “If you are asking me about belief in Allah, His angels, His Books, His messengers, the Last Day, Paradise, Hell, resurrection, and reckoning, then I believe in them. But if you are asking me about His saying, ‘Indeed, the believers are only those who, when Allah is mentioned, their hearts tremble,’ and the rest of the verse, then I do not know whether I am among them or not.”
Alqamah said: We were travelling when we met some people. We asked, “Who are you people?” They replied, “We are true believers.” We did not know what to answer them until we met Abdullah ibn Masud and informed him of what they had said. He asked, “What did you reply to them?” We said, “We gave them no reply.”