What virtue has been mentioned in Islamic law regarding the performance of the funeral prayer and following the funeral procession? What is the reward for doing so?

The funeral prayer entails great virtue and immense reward. It is among the rights of the deceased upon the living and is considered a communal obligation (farḍ kifayah). Islamic law emphasizes its importance and encourages believers to seize its reward. Abu Huraira (may Allah be pleased with him) reported that the Messenger of Allah (peace and blessings be upon him and his family) said, “Whoever follows a Muslim’s funeral out of faith and seeking its reward, and remains with it until the funeral prayer is performed and the burial is completed, will return with two qiraṭs of reward, each equivalent to Mount Uhud. And whoever performs the funeral prayer and then returns before burial, will return with one qiraṭ”
(Bukhari and Muslim).[1]

And Allah Almighty knows best.