In the second sentence of the verse...
In the second sentence of the verse, the reason of casting fear into the hearts of the disbelievers is stated such: "….for that they have associated with Allah for which He has sent down no authority,.." Finally, at the end of the verse, it has pointed out to the end of these people. It indicates that such people have done injustice to themselves and to their society; that is why: "…. and their abode is the Fire; and how bad is the abode of the unjust!
"And indeed Allah fulfilled His promise to you (in the first stage) when, with His leave, you slew them until when you became weak-hearted and disputed about the matter, and you disobeyed after that He showed you that which you loved. Some of you desire the world and some of you desire the Hereafter. Then He turned you away from them (the disbelievers) so He might try you.
And He has certainly forgiven you; and Allah is gracious to the believers." A Failure after Triumph In the explanation of the Battle of 'Uhud, it was said that at the beginning of the war, Muslims fought unitedly and with a special bravery so that they won the battle. But disobedience of a group of the strivers, who left their entrenchments and went to gather spoils of war, caused the circumstances to be changed and the troops of Islam bore a great failure.
When Muslim strivers, who had suffered to give many slain and a heavy loss, were returning to Medina, they were murmuring questions with each other as that: 'Had Allah not promised us the victory of the war? Then, why we were defeated in this war? So, in these verses, the Qur'an, answering them, explains the factors of their failure. This verse indicates that the promise of Allah about their triumph was completely right.
Therefore, at the beginning of fight they won the battle; and, by the command of Allah, they killed the enemies. The Qur'an tells them that this promise went on until the time they had not left the perseverance and following the command of the Prophet (S) . The failure began from the time weakness and disobedience came upon them.