Overall meaning :
Almighty Allah addresses His Prophet, Muhammad, may Allah bless him and grant him peace, saying: Are you not amazed that those who were told—after they enthusiastically asked for permission to fight their enemy— ‘Refrain now from fighting, perform the prescribed prayers and pay zakat.’ But as soon as fighting was prescribed for them, some of them feared the enemy just as they should fear Allah, or even more, saying, ‘Lord, why have you prescribed fighting for us? If only You would give us just a little more time!’ Allah then instructs His Prophet, Muhammad, may Allah bless him and grant him peace, to say to them: Trifling and transient are the pleasures of this life, but far better is the bliss in the life to come for those who fear Allah, and they will not be dealt with unjustly in the very least.
The Almighty proceeds to say that death will overtake all people wherever they may be, even if they barricade themselves in lofty impregnable fortresses. Regarding those who disbelieve the Messenger of Allah, may Allah bless him and grant him peace, Allah states that if good fortune comes their way, they say, ‘This is from Allah,’ but when harm befalls them, they say, ‘This is because of what Muhammad has brought.’ Hence, He instructs him to say to them that both the good and bad things that happen to them take place according to Allah’s foreknowledge and decree. What is the matter with these people that they scarcely understand what they are told?
Then, addressing His Prophet, Muhammad, may Allah bless him and grant him peace, He says to him: Whatever good happens to you is from Allah Almighty, but whatever evil and harm befalls you is from yourself. He further informs him that He has sent him to all mankind as a messenger to convey His message to them, and sufficient is Allah as a witness.