An-Nisa: 104
"And do not weaken..."
Do not become feeble, and do not falter.
"...in the pursuit of the people..."
In seeking out the disbelievers through combat and confronting them. Then, He binds them with the argument by His saying:
"If you are suffering..."
Meaning: The pain you endure from wounds and killing is not exclusive to you; it is a matter shared between you and them. It afflicts them just as it afflicts you. Furthermore, they endure it with patience and courage. So, why do you not endure as they endure, when you are more deserving of patience than they are, because:
"...you hope from Allah what they do not hope for."
Namely, the manifestation of your religion over all other religions, and the great reward in the Hereafter.
Al-A‘raj read “an takūnū ta’lamūn” (that you are suffering) with a fathah on the hamzah, meaning: "Do not weaken because you are suffering." His saying, "For they are suffering as you are suffering," is a justification. It has also been read as “fa-innahum yablūna kamā tablūn” (for they are being tested as you are being tested). It is narrated that this was regarding the Lesser Badr, where they had wounds and were hesitant.
"And Allah is ever Knowing, Wise."
He does not burden you with anything, nor does He command or forbid you, except for that which He knows will bring about your well-being.