Overall meaning :
Allah Almighty reassures His servants that they will incur no sin if they shorten the obligatory prayers while on a journey if they have reason to fear that the unbelievers will cause them harm by attacking them during the prayer, stating that the unbelievers show open enmity and bitter hostility towards them.
Then, addressing His Prophet, Muhammad, may Allah bless him and grant him peace, Allah Almighty instructs him that if he is on an expedition along with his companions and is in fear that the unbelievers might harm them, and stands to lead the prayer, he should divide them into two groups: one group rise up to pray with him, armed with their weapons, while the other group stand guard over them in the rear facing the enemy. After the group praying with him complete their prayers they should withdraw to the rear to stand guard facing the enemy, while the other group who have not prayed yet should come forward and join him for the rest of the prayer, also taking their precautions and holding on to their weapons. It would much please the unbelievers, Allah warns, if he believers neglect their arms and their equipment, so that they could swoop down on them with one assault and kill them all.
Allah then grants the faithful a concession, whereby they may lay down their arms, reassuring them that they will incur no sin if they do so if they are inconvenienced and bothered by rain or are sick, all the while taking adequate precautions, stating that He has prepared a humiliating punishment for the unbelievers in this life and in the life to come.
After they have completed their prayers in a state of fear, Allah further instructs Muslims, they should remember Him in all conditions, standing, sitting and lying on their sides. Then when they are once again secure, they should perform the prayer in full, declaring that the prayers is prescribed for the believers at fixed times.
Then He directs Muslims not to falter or relent in seeking out their enemies, for if they suffer pain and hardship, their enemies also suffer pain and hardship, and so they should not feel weaker than them, but the believers hope for victory, support and reward from Allah which the unbelievers cannot hope for. Surely Allah is All-Knowing, All-Wise.