They are joyful in the glad tidings of God’s blessing and bounty (that He has prepared for the martyrs), and in (the promise) that God never leaves to waste the reward of the believers
They are happy in the Grace and the plenty of good things from Allah, and in the fact that Allah does not cause the reward of the faithful to be lost (in the least)
And they (- the martyrs) are also receiving glad tidings (that those who have been left behind in the world are happy) because of the favours of Allah and (His) great bounty and that Allah does not suffer the reward of the believers to be lost
They are filled with joy owing to the blessing (of divine disclosures of the nearness) of Allah and His bounty (i.e., the pleasures of meeting with Him), and (also) because Allah does not waste the reward of the believers
They are filled with joy for the favour which they have received from God, and his bounty; and for that God suffereth not the reward of the faithful to perish
They want to share the blessings and bounty of Allah upon them and bring good tidings that the deeds of the believers will not be left unrequited.
Sayyed Abbas Sadr-Ameli
They rejoice because of favour from Allah and (His) grace, and that Allah does not waste the reward of the believers
Al-muntakhab fi tafsir al-Qur'an al-Karim
They have assumed a state of mind that brightens up their faces for the grace and the bounty conferred on them by Allah. It is a state of mind with an air of assurance that Allah does not withhold nor withdraw the grateful return due to those whose hearts have been impressed with the image of religious and spiritual virtues