Abbas - Tanwîr al-Miqbâs min Tafsîr Ibn ‘Abbâs
(So do not falter) do not weaken, O believer, upon fighting the disbelievers (and cry out for peace) and it is said this means: for Islam before fighting (when you (will be) the uppermost) when you are the victorious and the ultimate consequence will be in your favour, (and Allah is with you) He helps you to defeat your enemy, (and He will not grudge (the reward of) your actions) and He will not diminish the works in which you engage during jihad.
So do not falter, [do not] be weak, and [do not] call for peace (read salm or silm), that is to say, a truce with the disbelievers should you encounter them, when you have the upper hand (al-a‘lawna: the third letter of the triliteral root, wāw, has been omitted), [when you are] the victors, the vanquishers, and God is with you, helping and assisting, and He will not stint you, diminish you, in [the reward for] your works, that is to say, of the reward for them.
Nullifying the Disbelievers' Deeds and the Command to chase Them
Allah then informs about those who disbelieve, obstruct others from the path of Allah, oppose the Messenger and contend with him, and revert from the faith after guidance has become clear to them. He indicates that those people can never harm Allah in the least, and rather they only harm themselves and become losers on the Day of Resurrection. He will nullify their deeds. Allah will not reward them even the weight of a mosquito (i.e., the smallest thing) for any good that they did before their apostasy, but would instead totally invalidate and destroy it. Their apostasy wipes away their good deeds entirely, just as the good deeds would normally wipe away the evil deeds. Imam Ahmad Ibn Nasr Al-Marwazi reported in Kitab As-Salah (the Book of Prayer) that Abu Al-`Aliyah said, "The Prophet's Companions used to think that no sin would harm a person who says `La ilaha illallah,' just as no good deed would benefit a person who joins partners with Allah. So Allah revealed,
(Obey Allah and obey the Messenger and do not invalidate your deeds.) This made them fear that some sins could nullify their deeds.'' It has also been reported from Ibn `Umar, may Allah be pleased with him, that he said, "We, the Companions of Allah's Messenger, used to think that good deeds would all be accepted, until Allah revealed,
(Obey Allah and obey the Messenger and do not invalidate your deeds. ) So we asked each other: `What is it that can nullify our deeds' So we said, `The major sins, great offenses that require admission into the Fire and immoral sins.' But then Allah revealed,
(Verily, Allah does not forgive joining partners with Him in worship, but He forgives except that to whom He wills.) (4:48) After this was revealed, we ceased saying that. We thereafter continued to fear for those who committed great sins and immoral sins and to have hope for those who did not.'' Then, Allah commands His believing servants to obey Him and His Messenger, which would result in their happiness in this worldly life and the Hereafter. He also prohibits them from apostasy, because that would result in the nullification of their deeds. Thus He says,
وَلاَ تُبْطِلُواْ أَعْمَـلَكُمْ
(and do not invalidate your deeds.) meaning, by apostasy. Thus, Allah says after this,
(So do not lose heart and beg for peace while you are superior.) meaning, in the condition of your superiority over your enemy. If, on the other hand, the disbelievers are considered more powerful and numerous than the Muslims, then the Imam (general commander) may decide to hold a treaty if he judges that it entails a benefit for the Muslims. This is like what Allah's Messenger did when the disbelievers obstructed him from entering Makkah and offered him treaty in which all fighting would stop between them for ten years. Consequently, he agreed to that. Allah then says:
(And Allah is with you) This contains the good news of victory and triumph over the enemies.
وَلَن يَتِرَكُمْ أَعْمَـلَكُمْ
(and He will never deprive you of (the reward of) your deeds.) meaning, Allah will never invalidate your deeds, nullify them, or deprive you of them, but rather He will give you your rewards complete, without any reduction.'' And Allah knows best.
Maududi - Sayyid Abul Ala Maududi - Tafhim al-Qur'an
This sentence has two meanings:
(1) That Allah will render vain and fruitless all those works which they had performed as "good works", and they will get no reward whatever for them in the Hereafter; and
(2) that all the devices that they are adopting to obstruct the way of Allah and His Messenger's Religion will prove ineffective and fruitless.
In other words, the deeds' being beneficial and yielding of good results depends wholly on one's obedience to Allah and His Messenger. After one has turned away from obedience, no deed remains a good deed so that one may deserve any reward for it.
Here, one should bear in mind the fact that when this discourse was revealed only a handful of the Muslims consisting of a couple of hundreds of the Muhajirin and Ansar living in the small town of Madinah were upholding the standard of Islam and they were not only faced by the powerful Quraish but also by the whole of pagan Arabia. Such were the conditions when they were exhorted 'not to be faint-hearted and not to beg (the enemy) for peace", but to make preparations for the decisive conflict. This does not mean that the Muslims should never negotiate for peace, but it means that in a state like this it is not right to initiate peace negotiations when it shows the Muslims' weakness, for it will still further embolden the enemy. The Muslims should first establish their superiority in power and strength; then if they negotiate peace there will be no harm.
That is, "As against the Hereafter, this world is no more than a means of temporary entertainment. The success or failure here is not anything real and enduring, which might in any way be important. The real life is life hereafter success in which should be man's main concern. (For further explanation, see E.N. 102 of Surah AI-`Ankabut).
That is, "Allah is Self-Sufficient: He does not need taking anything from you for His own Self. If He tells you to expend something in His way, He does so not for Himself but only for your own good."
That is, "He does not put you to any severe trial that may bring out your weaknesses. "