{فَرِحِينَ} {Rejoicing}: Why does Allah (swt) mention the state of joy that surrounds them? Because the atmosphere of sadness surrounds the families of the martyrs who scarify by themselves, their blood and their souls, so Allah (swt) wants to reassure the families and beloved of the martyrs that: Their martyrs are happy, so why do their families grieve?
فَرِحِينَ بِمَا آتَاهُمُ اللّهُ مِن فَضْلِهِ{Rejoicing in what Allah has bestowed upon them of His bounty}: He said: (of His bounty), not of his justice. Bounty is above justice; justice is to be awarded according to work, as Allah (swt) says:
وَنَضَعُ الْمَوَازِينَ الْقِسْطَ لِيَوْمِ الْقِيَامَةِ فَلَا تُظْلَمُ نَفْسٌ شَيْئًا وَإِن كَانَ مِثْقَالَ حَبَّةٍ مِّنْ خَرْدَلٍ أَتَيْنَا بِهَا وَكَفَى بِنَا حَاسِبِينَ
{And We place the scales of justice for the Day of Resurrection, so no soul will be treated unjustly at all. And if there is [even] the weight of a mustard seed, we will bring it forth. And sufficient are We as accountant.} (Al-Anbiyaa: 47)
This is justice, as for bounty, is more than what a person deserves, so what honor is this for the one who offered himself, his soul, and his blood as a sacrifice for his country, his religion, his sanctities, his honor and his money. There is nothing other than this Qur’anic expression that comforts the hearts of the bereaved with their martyrs more than this saying:
فَرِحِينَ بِمَا آتَاهُمُ اللّهُ مِن فَضْلِهِ {Rejoicing in what Allah has bestowed upon them of His bounty}
Not only this but He (swt) says:
وَيَسْتَبْشِرُونَ بِالَّذِينَ لَمْ يَلْحَقُواْ بِهِم مِّنْ خَلْفِهِمْ {an d they receive good tidings about those [to be martyred] after them who have not yet joined them}: Receiving good tidings in Arabic refers to joy, and it is taken (in Arabic) from the complexion because when a person is happy, his complexion shins.
أَلاَّ خَوْفٌ عَلَيْهِمْ {there will be no fear concerning them}: Grief is for what has happened, for those who are after them from among the believers, are either afraid of this fate of being killed, or they are grieve for the loss of loved ones.