فِي قُلُوبِهِم مَّرَضٞ فَزَادَهُمُ ٱللَّهُ مَرَضٗاۖ وَلَهُمۡ عَذَابٌ أَلِيمُۢ بِمَا كَانُواْ يَكۡذِبُونَ ١٠
In their hearts is disease, so Allāh has increased their disease;1 and for them is a painful punishment because they [habitually] used to lie.
Translation: Saheeh International (English)
1 The "disease" mentioned here includes doubt, hypocrisy, arrogance and disbelief.
Each word's meaning and sound
Allah increases the disease in their hearts, and they reap what they sow. Because they lied Allah increases the disease of doubts in their hearts, by adding hesitation to their uncertainty, hence they only gain what they deserve. They will have a painful suffering in the worst parts of Hell because they lied against Allah, and the people, and rejected the message brought by Muhammad (peace be upon him).
Al-Mukhtasar in interpreting the Noble Quran