Allah states that He has compensated His believing servants for their lives and wealth -- if they give them up in His cause -- with Paradise. This demonstrates Allah's favor, generosity and bounty, for He has accepted the good that He already owns and bestowed, as a price from His faithful servants. Al-Hasan Al-Basri and Qatadah commented, "By Allah! Allah has purchased them and raised their worth." Shimr bin `Atiyyah said, "There is not a Muslim but has on his neck a sale that he must conduct with Allah; he either fulfills its terms or dies without doing that." He then recited this Ayah. This is why those who fight in the cause of Allah are said to have conducted the sale with Allah, meaning, accepted and fulfilled his covenant. Allah's statement,
يُقَـتِلُونَ فِى سَبِيلِ اللَّهِ فَيَقْتُلُونَ وَيُقْتَلُونَ
(They fight in Allah's cause, so they kill and are killed.) indicates that whether they were killed or they kill the enemy, or both, then Paradise will be theirs. The Two Sahihs recorded the Hadith,
«وَتَكَفَّلَ اللهُ لِمَنْ خَرَجَ فِي سَبِيلِهِ لَا يُخْرِجُهُ إِلَّا جِهَادٌ فِي سَبِيلِي وَتَصْدِيقٌ بِرُسُلِي بِأَنْ تَوَفَّاهُ أَنْ يُدْخِلَهُ الْجَنَّةَ، أَوْ يَرْجِعَهُ إِلَى مَنْزِلِهِ الَّذِي خَرَجَ مِنْهُ، نَائِلًا مَا نَالَ مِنْ أَجْرٍ أَوْ غَنِيمَة»
(Allah has made a promise to the person who goes out (to fight) in His cause; `And nothing compels him to do so except Jihad = in My Cause and belief in My Messengers. ' He will either be admitted to Paradise if he dies, or compensated by Allah, either with a reward or booty if He returns him to the home which he departed from.) Allah's statement,
وَعْدًا عَلَيْهِ حَقًّا فِي التَّوْرَاةِ وَالإِنجِيلِ وَالْقُرْءانِ
(It is a promise in truth which is binding on Him in the Tawrah and the Injil and the Qur'an.) affirms this promise and informs us that Allah has decreed this for His Most Honorable Self, and revealed it to His Messengers in His Glorious Books, the Tawrah that He sent down to Musa, the Injil that He sent down to `Isa, and the Qur'an that was sent down to Muhammad ﷺ, may Allah's peace and blessings be on them all. Allah said next,
وَمَنْ أَوْفَى بِعَهْدِهِ مِنَ اللَّهِ
(And who is truer to his covenant than Allah) affirming that He never breaks a promise. Allah said in similar statements,
وَمَنْ أَصْدَقُ مِنَ اللَّهِ حَدِيثاً
(And who is truer in statement than Allah)4:87, and,
وَمَنْ أَصْدَقُ مِنَ اللَّهِ قِيلاً
(And whose words can be truer than those of Allah)4:122. Allah said next,
فَاسْتَبْشِرُواْ بِبَيْعِكُمُ الَّذِى بَايَعْتُمْ بِهِ وَذَلِكَ هُوَ الْفَوْزُ الْعَظِيمُ
(Then rejoice in the bargain which you have concluded. That is the supreme success.), meaning, let those who fulfill the terms of this contract and uphold this covenant receive the good news of great success and everlasting delight.