Tafsir of Ghafir 40:82

{And traces} Their palaces and their industrial works. It is also said: their walking on their feet, due to the immense size of their bodies.

{So what did avail them} The ma (what) is either negative or implies the meaning of an interrogation; its place is in the accusative. The second ma is either relative or infinitive, and its place is in the nominative. It means: what thing did their earnings or their acquisition avail them?

{They rejoiced in what they had of knowledge} There are several interpretations:

1. Sarcasm: It refers to the knowledge mentioned by way of mockery in His saying: “Rather, their knowledge is exhausted regarding the Hereafter” (An-Naml: 66). Their knowledge regarding the Hereafter was that they used to say: "We will not be resurrected, nor will we be punished," and "I do not think the Hour will occur," and "If I am returned to my Lord, I will surely have the best with Him." They rejoiced in this and used it to repel the clear proofs and the knowledge of the Prophets, as He, the Almighty, said: “Every faction rejoicing in what they have” (Ar-Rum: 32).
2. The Philosophers: It refers to the knowledge of the philosophers and the materialists (Dahriyyun) among the Greeks. When they heard of God’s revelation, they rejected it and belittled the knowledge of the Prophets compared to their own. It is narrated of Socrates that he heard of Moses (peace be upon him), and it was said to him, "If only you would emigrate to him," to which he replied, "We are a refined people; we have no need of one to refine us."
3. Hyperbole in Negation: Placing the phrase “They rejoiced in what they had of knowledge”—when they had no knowledge at all—in place of "they rejoiced in what came to them of knowledge." This is a hyperbole in denying their joy in the revelation (which is the source of ultimate joy), while mocking their extreme ignorance and lack of true scholars.
4. Mockery of the Messengers: It means they rejoiced in the knowledge the Messengers possessed with a joy of laughter and mockery. It is as if it said: They mocked the clear proofs and the knowledge of revelation they brought, while being joyful and insolent. This is supported by His saying: “And they were encompassed by what they used to mock.”
5. Joy of the Messengers: The joy is attributed to the Messengers. It means that when the Messengers saw their persistent ignorance and mockery of the truth, and knew the evil of their end and the punishment that would befall them for their ignorance and mockery, they rejoiced in the knowledge they were given and thanked God for it. Meanwhile, the punishment for their ignorance and mockery encompassed the disbelievers.
6. Worldly Knowledge: It may mean the knowledge they rejoiced in was their knowledge of worldly affairs and their expertise in managing them, as He said: “They know what is apparent of the worldly life, but they are, of the Hereafter, unaware” (Ar-Rum: 7), and “That is their sum of knowledge” (An-Najm: 30). When the Messengers came to them with the knowledge of religion—which was the furthest thing from their own knowledge because it calls for the rejection of the world and abstinence from pleasures and desires—they paid no attention to it, belittled it, and mocked it, believing that no knowledge was more beneficial or profitable than their own, so they rejoiced in that.

{And when they saw Our punishment, they said, "We believe in Allah alone and disbelieve in what we used to associate with Him." But never did their faith benefit them when they saw Our punishment. [It is] the established way of Allah which has preceded among His servants. And there, the disbelievers lost.}