What is the meaning of Umar ibn Abd al-Aziz's saying: "A man who sells his afterlife for the worldly gain of another"?

It was reported from the Salaf and early Imams that the most foolish, or most bankrupt, or most wretched of people, is he who sells his Hereafter for the worldly life of another. This statement was attributed to the Prophet, peace and blessings be upon him, though its authenticity as a Prophetic Hadith is not confirmed. However, another Hadith was reported from Abu Sa'id al-Khudri that a Bedouin sold a sheep, and when this was mentioned to the Prophet, peace and blessings be upon him, he said: "He sold his Hereafter for his worldly life." Al-Albani graded it as good (hasan).

The meaning of "he sold his Hereafter for his worldly life" is committing sins for the sake of worldly gain, which exposes the person to losing the bliss of the Hereafter. As for "he sold his Hereafter for the worldly life of another," this is used for someone who disobeys Allah and loses the Hereafter, not for himself, but for someone else. Examples include one who assists an oppressor, or a corrupt scholar who aids unjust rulers. Such a person is considered the most bankrupt, because he lost his Hereafter and gained nothing from this world.