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,
أَطِيعُواْ اللَّهَ وَأَطِيعُواْ الرَّسُولَ وَلاَ تُبْطِلُواْ أَعْمَـلَكُمْ
(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 ﷺ, used to think that good deeds would all be accepted, until Allah revealed,
أَطِيعُواْ اللَّهَ وَأَطِيعُواْ الرَّسُولَ وَلاَ تُبْطِلُواْ أَعْمَـلَكُمْ
(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,
إِنَّ اللَّهَ لاَ يَغْفِرُ أَن يُشْرَكَ بِهِ وَيَغْفِرُ مَا دُونَ ذَلِكَ لِمَن يَشَآءُ
(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,
إِنَّ الَّذِينَ كَفَرُواْ وَصَدُّواْ عَن سَبِيلِ اللَّهِ ثُمَّ مَاتُواْ وَهُمْ كُفَّارٌ فَلَن يَغْفِرَ اللَّهُ لَهُمْ
(Verily, those who disbelieved and obstructed others from the path of Allah and then died as disbelievers -- never will Allah forgive them.) This is similar to His saying,
إِنَّ اللَّهَ لاَ يَغْفِرُ أَن يُشْرَكَ بِهِ وَيَغْفِرُ مَا دُونَ ذَلِكَ لِمَن يَشَآءُ
(Verily, Allah does not forgive joining partners with Him in worship, but He forgives except that to whom He wills.) (4:48) Allah then addresses His believing servants by saying,
فَلاَ تَهِنُواْ
(So do not lose heart) meaning, do not be weak concerning the enemies.
وَتَدْعُواْ إِلَى السَّلْمِ
(and beg for peace) meaning, compromise, peace, and ending the fighting between you and the disbelievers while you are in a position of power, both in great numbers and preparations. Thus, Allah says,
فَلاَ تَهِنُواْ وَتَدْعُواْ إِلَى السَّلْمِ وَأَنتُمُ الاٌّعْلَوْنَ
(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 ﷺ 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:
وَاللَّهُ مَعَكُمْ
(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.