Commentary
The event of the battle of Badr which has been described in a somewhat detailed manner in the previous verses contains many lessons in hard advice and wisdom both for those who adhere to Islam and those who stick to disbelief. These appear intermittently during the course of relevant narrations and serve as warning signals.
For example, in the previous verses, after having recounted the defeat and disgrace of the disbelievers of Makkah, it was said: ذَٰلِكَ بِأَنَّهُمْ شَاقُّوا اللَّـهَ وَرَسُولَہ (That is because they were hostile to Allah and His Messenger - 13). It means that the disbelievers of Makkah were defeated despite their numerical and logistic strength and the real reason behind it was that they had elected to act hostile to Allah and His Messenger. In this, there lies a chastening lesson for people who bypass the most perfect power of the Creator and Master of the heavens and the earth - the power that is visible and the power that is invisible - and who opt for placing their reliance on material strengths only, or just choose to cheat their own selves by hoping and praying that the help and support of Allah will be by their side despite all their acts of disobedience to Him.
In the present verse, the other side of this very problem has been taken up by addressing Muslims. Stated briefly, the truth of the matter is that Muslims were blessed with this great victory despite their low numbers and ill-equipped fighting force only through the help and support of Allah Almighty - and this Divine help and support is the outcome of their obedience to Allah. This obedience is what Muslims have been obligated with and to this they have to adhere firmly: يَا أَيُّهَا الَّذِينَ آمَنُوا أَطِيعُوا اللَّـهَ وَرَسُولَهُ ( O those who believe, obey Allah and His Messenger). In the sentence which follows, the same subject has been further emphasized by saying: وَلَا تَوَلَّوْا عَنْهُ وَأَنتُمْ تَسْمَعُونَ (and do not turn away from him while you are listening). The sense is that once you have listened to the Qur'an, the true word of Allah, do not go about doing things against the norms of genuine obedience.
Listening denotes listening to what is the truth and it has four degrees in terms of effective response. (1) The hearer with ears simply heard some voice but neither tried to understand it, nor understood it, nor believed in or relied upon it, nor did he act accordingly. (2) He heard it through his ears all right, even understood it, but did neither believe in it nor acted accordingly. (3) He heard, he understood, even believed and trusted, but did not act accordingly. (4) He heard, he understood, he believed, he trusted - and acted accordingly as well.
It is obvious that the real purpose of listening is fully realized only through the fourth degree - which is the station of perfect believers. As for the earlier three degrees, the act of listening described there is imperfect and incomplete which, in a manner of saying, could be set aside as just not listening - as readily pointed to in the verses appearing next. The third degree mentioned above has the ingredients of hearing the truth, understanding it and believing in it, but lacks corresponding deeds. Here, the real purpose of listening is though not realized as it should be, yet belief has its own importance and cannot be rejected as useless. This degree pertains to sinning Muslims. Then there is the second degree where we find only listening and under-standing but no belief and no corresponding deed. This degree is that of the munafiqin (hypocrites) for they do listen to the Qur'an, understand it too, even have a feigned claim to desired belief and deed, but the reality is that they do not believe and do what is right and due. Finally, the first degree is that of polytheists and disbelievers who listened to the message of truth and the 'ayat of the Qur'an with their own ears but were never motivated enough to understand and think about that.
In the verse cited above (20), the address is to Muslims who have been told that they do listen to the message of truth after all, that is, the initial requirement of listening, understanding and believing is present in their attitude as it is, but they have to do more than that. They must act, do what must be done and do it fully and faithfully. They have been asked not to do anything which would take them away from the path of obedience so that the real purpose of listening to the word of truth stands realized fully.