Here it refers to their weakness of will-power...

Here it refers to their weakness of will-power, carelessness in establishing the religion and lack of courage in face of its enemies. al-Huzn (grief ) is opposite of al-farh (joy, happiness); it afflicts a man when he loses a favorite possession, or something which he thinks belongs to him. The words, "and you shall have the upper hand if you are believers".

If a wound has afflicted you (at Uhud), a wound like it has also afflicted the (unbelieving) people;', indicate that the believers had felt infirmity and grief because they had seen themselves afflicted by wounds and found the unbelievers gaining upper hand.

Although the polytheists could not get total victory over the believers, nor the battle ultimately ended with the believers' decisive defeat, yet what had afflicted them was really hard and painful - martyrdom of seventy of their brave warriors. Add to it the humiliation that they had been overwhelmed on their own ground. All these factors together had caused extreme dejection and pessimism.

The clause, "and you shall have the upper hand if you are believers" (which stands as the reason of these two prohibitions), shows that the prohibition was related to actual infirmity and grief, not to some expected behavior in future. The promise, "you shall have the upper hand", is general and unrestricted, but it is followed by the proviso, "if you are believers".

It therefore gives the following meaning: You should not be weak in your will-power, nor should you grieve for the lost victory, if you are true believers. It is because belief - is bound to give you upper hand over your enemies - belief is accompanied by piety and patience, and these two are the basis of victory and triumph. As for the wound, which has afflicted you in this battle, you are not alone in it; the unbelievers too had suffered similar casualties.

If you think it over, they have not gained over you in any way. Therefore, you should not feel depressed or grieved. The address had started with the words, O you who believe; yet their gaining upper hand has been made conditional on their being believers. It implies that although the masses were not devoid of faith and belief, they had not adhered to the concomitants and requirements of that belief, like patience and piety; otherwise it would have brought out the desired effects.