In The Name of Allaah, The Most Merciful, The Bestower of Mercy.
Al-Allaamah Rabee Bin Haadee Al-Madkhalee [hafidhahullaah] said:
Let us increase in obedience to [Allaah]. Let us be mindful of Shubuhaat [i.e. affairs that are made to resemble the truth but are falsehood in reality] and Shahawaat [i.e. vain desires or impermissible desires], for indeed the Fitan [trials and tribulations] will be exposed to the hearts. Hudhaifah [radiyallaahu-anhu] reported from Allaah’s Messenger [sallal-laahu-alayhi-wasallam] who said, “The Fitan will be presented to the hearts of the people like a reed mat woven stick by stick, and any heart afflicted by them will have a black mark put into it, but any heart that rejects them will have a white mark put into it. Thus there will be two kinds of hearts: one is pure like a white gemstone and it will not be harmed by any tribulation as long as the heavens and earth endure, and the other is black and dusty like a worn-out vessel, neither recognizing good nor rejecting evil, but rather immersed in its desires.” [Saheeh Muslim’ Number 144]
The first type of heart: Pure like a white gemstone and it will not be harmed by any tribulation as long as the heavens and earth endure. That is because Allaah grants them firmness and not due to their own power or strength; rather Allaah grants them firmness, just as [Allaah stated in the Aayah we quoted]: Allah will keep firm those who believe, with the word that stands firm in this world (i.e. they will keep on worshipping Allah Alone and none else), and in the Hereafter. [Surah Ibraaheem’ Aayah 27]
Allaah bestows His favour upon them by granting them firmness, so they are not harmed regardless the greatness of the Fitan.
Let me strike a similitude: I say, indeed amongst the people in the midst of these Fitan – just as Allaah’s Messenger [alayhis salaatu wassalaam] described the situation- are those who are firm like mountains; the winds, floods, hurricanes and storms come along, but they do not shake, because the Eemaan in the hearts [of these people] is like the firm mountains. Allaah keeps them away from the Fitan and makes them firm, so they are not harmed. However, there are other people who are like the trees that are moved -by the wind – to the right and the left until they finally fall. And there are others who are like feathers and the Henna leaves- flying along with the Fitan when little Fitna occurs, such as when a mild wind [blows] the fragile leaves to a far off place. We ask Allaah to keep us firm.
The second type of heart: It is described [as follows]: ‘’Black and dusty like a worn-out vessel, neither recognizing good nor rejecting evil, but rather immersed in its desires.” This is the state of the one whose heart is immersed in Fitnah. He agrees with it and does not reject it, so the Fitnah enters him gradually until his heart is worn-out and thus becomes black like a worn-out vessel – a vessel whose mouth is turned upside down, so regardless the amount of water, butter fat and other things one attempts to pour into it, it will not accept anything. Indeed, we have often experienced the affair of this category of people – whose hearts are worn-out – and regardless the [number] of proofs and evidences- from the Qur’aan and Sunnah – presented to nullify their falsehood, they do not accept that from you. This has to be the case because indeed Allaah’s Messenger [alayhis salaatu wassalaam] described such a person as one with a heart that is similar to a worn-out vessel- a heart that neither recognises truth nor rejects evil; rather it is immersed in its desires. Whatever agrees with his desires, he accepts it- not because it is the truth, rather only because it agrees with his desires. This [behaviour] is similar to that of the Yahood [i.e. those Yahood who rejected the clear message of the final Messenger], for they know the truth, but wage war against it – accepting what agrees with their desires and rejecting what opposes their desires and wage war against it. This is something rife in this era amongst those whose hearts are worn-out and thus they reach this state that has been described by Allaah’s Messenger [alayhis salaatu wassalaam]. It is as if we are witnessing this affair whilst Allaah’s Messenger describes these people -in our presence- and we can see their deeds and dishonourable stances.
Source: Marhaban Yaa Taalibal Ilm’ pages 206-208. slightly paraphrased