Allah commands His faithful servants to take precautions against their enemies, by being prepared with the necessary weapons and supplies, and increasing the number of troops fighting in His cause.
(in parties) means, group after group, party after party, and expedition after expedition. `Ali bin Talhah reported that Ibn `Abbas said that,
(and either go forth in parties) means, "In groups, expedition after expedition,
(or go forth all together), means, all of you." Similar was reported from Mujahid, `Ikrimah, As-Suddi, Qatadah, Ad-Dahhak, `Ata' Al-Khurrasani, Muqatil bin Hayyan and Khusayf Al-Jazari.
Allah said,
(There is certainly among you he who would linger behind.) Mujahid and others said that this Ayah was revealed about the hypocrites. Muqatil bin Hayyan said that,
(linger behind) means, stays behind and does not join Jihad. It is also possible that this person himself lingers behind, while luring others away from joining Jihad. For instance, `Abdullah bin Ubayy bin Salul, may Allah curse him, used to linger behind and lure other people to do the same and refrain from joining Jihad, as Ibn Jurayj and Ibn Jarir stated. This is why Allah said about the hypocrite, that when he lingers behind from Jihad, then:
(If a misfortune befalls you) death, martyrdom, or - by Allah's wisdom - being defeated by the enemy,
(he says, "Indeed Allah has favored me that I was not present among them.") meaning, since I did not join them in battle. Because he considers this one of Allah's favors on him, unaware of the reward that he might have gained from enduring war or martyrdom, if he was killed.
(But if a bounty comes to you from Allah) such as victory, triumph and booty,
(he would surely say - as if there had never been ties of affection between you and him,) meaning, as if he was not a follower of your religion,
("Oh! I wish I had been with them; then I would have achieved a great success.") by being assigned a share of the booty and taking possession of that share. This is his ultimate aim and objective.
Allah then said,
(So fight) the believer with an aversion (to fighting),
(those who trade the life of this world with the Hereafter) referring to those sell their religion for the meager goods of the world, and they only do this because of their disbelief and lack of faith. Allah then said;
(And whoever fights in the cause of Allah, and is killed or gets victory, We shall bestow on him a great reward.) meaning, whoever fights in the cause of Allah, whether he was killed or triumphant, he will earn an immense compensation and a great reward with Allah. The Two Sahihs recorded,
(Allah has guaranteed the Mujahid in His cause that He will either bring death to him, admitting into Paradise; or, He will help him return safely to his home with whatever reward and booty he gained.)