In The Name of Allaah, The Most Merciful, The Bestower of Mercy

Allaah [The Most High] said:

لَا تَحۡسَبَنَّ ٱلَّذِينَ يَفۡرَحُونَ بِمَآ أَتَواْ وَّيُحِبُّونَ أَن يُحۡمَدُواْ بِمَا لَمۡ يَفۡعَلُواْ فَلَا تَحۡسَبَنَّہُم بِمَفَازَةٍ۬ مِّنَ ٱلۡعَذَابِ‌ۖ

وَلَهُمۡ عَذَابٌ أَلِيمٌ۬

Think not that those who rejoice in what they have done (or brought about), and love to be praised for what they have not done,- think not you that they are rescued from the torment, and for them is a painful torment.” [3:188]

Imaam Ibnul Qayyim [rahimahullaah] said: They rejoice in what they have brought about of bidah and misguidance, and love to be praised for following the Sunnah and sincerity. [i.e. they want to be praised for what they do not deserve with regards to following the sunnah and having sincerity] [1]

Imaam As-Sadi [rahimahullaah] said: They want to be praised for that which they have not done and [praised for some] truthful [statement] they have not uttered; so they combine evil doing and its statement, and rejoice in that. And they love to be praised for some good they have not done. [2]

Obstinate Disbelievers Rejoice Due to The Temporary Things of The Worldly Life

Allaah [The Most High] said:

قُلۡ بِفَضۡلِ ٱللَّهِ وَبِرَحۡمَتِهِۦ فَبِذَٲلِكَ فَلۡيَفۡرَحُواْ هُوَ خَيۡرٌ۬ مِّمَّا يَجۡمَعُونَ

Say: “In the Bounty of Allah, and in His Mercy; -therein let them rejoice.” That is better than what (the wealth) they amass.’’ [Yonus: Ayah 58]

[قُلۡ بِفَضۡلِ ٱللَّهِ -Say: In the Bounty of Allaah]- Meaning: the Qur’aan, which is the greatest blessing and favour, and a conferment by way of which Allaah preferred His [believing] slaves [over others]; [وَبِرَحۡمَتِهِ -And in His Mercy]-Meaning: The Religion [of Islaam], Eemaan, worship of Allaah, love of Him, and knowledge and awareness of Him; [فَلۡيَفۡرَحُواْ- Therein let them rejoice]; [هُوَ خَيۡرٌ۬ مِّمَّا يَجۡمَعُونَ – That is better than what they amass] of the enjoyable things of the worldly life and its pleasures.

The religion- the bounty that will bring about happiness in this life and the next- cannot be compared to all that is in this worldly life, [because these things of the worldly life] will vanish and come to an end very soon.  Rather Allaah [The Most High] commanded [us] to rejoice in His Bounty and Mercy because it is that which will make the soul happy, thankful to Allaah, gives it a strong desire for an increase in knowledge and Eemaan. This is a praiseworthy rejoicing as opposed to rejoicing in the desires of this worldly life and its pleasures, or rejoicing in falsehood, for indeed that is blameworthy, as Allaah [The Most High] stated about a group amongst the people of Qaaroon that they said to him:

[لَا تَفۡرَحۡ‌ۖ إِنَّ ٱللَّهَ لَا يُحِبُّ ٱلۡفَرِحِينَ- Do not be glad (with ungratefulness to Allah’s Favours). Verily! Allah likes not those who are glad (with ungratefulness to Allah’s Favours)] [Soorah Al-Qasas: Ayah 76].

And as Allaah [The Most High] said about those who rejoiced in what they possessed of falsehood in opposition to that which the Messengers came with: [فَلَمَّا جَآءَتۡهُمۡ رُسُلُهُم بِٱلۡبَيِّنَـٰتِ فَرِحُواْ بِمَا عِندَهُم مِّنَ ٱلۡعِلۡمِ -Then when their Messengers came to them with clear proofs, they were glad (and proud) with that which they had of the knowledge (of worldly things)] [Soorah Ghaafir: Ayah 83] [3][

[1] Madaarij as-Saalikeen 1/84. slightly paraphrased]

[2] An Excerpt from ‘Tayseer Al-Kareem ar-Rahmaan Fee Tafseer Kalaam al-Mannaan’. slightly paraphrased]

[3: An Excerpt from ‘Tayseer Al-kareem Ar-Rahmaan Fee Tafseer Kalaam Al-Mannaan). slightly paraphrased]