Translation:

66. If only they had stood fast by the Law the Gospel and all the revelation that was sent to them from their Lord they would have enjoyed happiness from every side. There is from among them a party on the right course; but many of them follow a course that is evil.

Notes (Tafseer)

776. To eat (akala) is a very comprehensive word, and denotes enjoyment generally, physical, social, mental and moral, and spiritual. "To eat what is forbidden" in verses 62 and 63 referred to taking unlawful profit, from usury or trust funds or in other ways. Here "eating" would seem to mean receiving satisfaction or happiness in this life as well as in the life to come. "From above them" may refer to heavenly or spiritual satifaction, and "from below their feet" to earthly satisfaction. But it is better to take the words as a general idiom, and understand "satisfaction or happiness from every side."