Abbas - Tanwîr al-Miqbâs min Tafsîr Ibn ‘Abbâs
(And if We cause him) i.e. the disbeliever (to taste grace after some misfortune) after some hardship (that had befallen him, he saith) i.e. the disbeliever: (The ills) hardships (have gone from me. Lo! he is exultant) arrogant, (boastful) about Allah's blessings and does not give thanks;
But if We cause him to taste prosperity after some misery, [such as] impoverishment and hardship, that had befallen him, assuredly he will say, ‘The ills, the afflictions, have gone from me’, when he had not anticipated that they would go away; yet still he does not give thanks for this; lo!, he is exultant, wanton, boastful, to people of what he has been given;
Maududi - Sayyid Abul Ala Maududi - Tafhim al-Qur'an
This disgraceful characteristic of man has been mentioned here because the disbelievers were exhibiting it at that time. When the Holy Prophet warned them of the consequences of their disobedience to Allah, they would scoff at hire as if to say, "Arc you mad? Can't you see our prosperity and power? We are enjoying all the good things of life and dominating over everything and everyone all around us. How is it that you are prophesying torment for us?"
The above-mentioned arrogant behavior was due to the disgraceful human characteristic which has been mentioned in this verse. It is this: Man is, by nature, shallow and superficial and lacks the depth of thought. Therefore, when he enjoys prosperity and power he becomes joyous, arrogant and boastful; so much so that he never even dreams of any possibility that his happy condition would ever come to an end. And if and when adversity befalls him, he becomes an embodiment of despair and begins to complain of his misfortune here, there, and everywhere; so much so that he does not hesitate even to abuse God and taunt at His Godhead. But whenever there is a change for the better in his fortune, he again begins to brag of his foresight, wisdom and success. That is why the disbelievers were exhibiting such a shallow and superficial characteristic in answer to the warning of the Holy Prophet. They forgot that Allah was deferring their punishment because of His mercy to give them sufficient time to consider well their absurd attitude and mend their ways during the respite given to them, and not to delude themselves by imagining that their prosperity had very deep foundations and would last for ever.
Here (sabr) (fortitude) implies another meaning also, that is, "steadfastness" the antonym of shallowness etc., that has been mentioned in the preceding verse. Those "who are steadfast" remain fine and unwavering in their purpose in spite of the vicissitudes of life. They are not influenced by the changes of circumstances, but stick to the right, reasonable and correct attitudes they have adopted. They do rot give themselves airs nor become intoxicated nor over-jubilant and boastful, if they win power, prosperity and name. On the contrary, they are neither subdued nor depressed if they are visited by adversity. In short, they come out successful in their trial by Allah, whether it be in the shape of favor or adversity and remain steadfast in both the cases.
This is the favor that Allah shows to such people; He forgives their shortcomings and gives them rich rewards for their good deeds.