Imām Abū al-Farj ibn al-Jawzī (d. 597 AH) said:

[Among the ways of dealing with catastrophe, misfortune, sadness, and depression in this life] is that [a Muslim] should imagine how his joyful excursion in Jannah will be never ending. What is the true value of that moment [of entry]? Rather, what is the true value of this entire [temporal] existence compared to the eternal, everlasting life [of the hereafter]?

To further clarify this, [the parable of the eternal nature of the hereafter is like] if Allāh the Glorified, the Most High, was to cover the heavens and the earth and everything that is between them with mustard seeds, and then He created a single bird whom He ordered to transfer this mustard seed once every million years, imagine how long it would take for [the seeds] to finish. [Except that] the existence of the people of Jannah will never end.

[One must] truly imagine eternal life and his existence in eternal enjoyment just as his Creator the Exalted is eternal, His existence never coming to an end. [Truly comprehending this] causes immediate unbridled happiness and allows one to forget that which pains him. If death represents the only path towards such enjoyment, it should be welcomed [when it arrives].

Narrated by Abū Saʿīd and Abū Hurayrah (may Allāh be pleased with both of them) that the Prophet (ﷺ) said:

‘The people of Jannah will be called: Indeed, you may live and never experience death [again]. Indeed, you may attain true health and shall never experience [the darkness of] ailments [of any kind again]. Indeed, you may bask in eternal youth for you shall never experience old age [again]. Indeed, you may now experience true enjoyment for you shall never despair [again].’

 
Source: Al-Thabāt: 52
Translated by: Riyāḍ al-Kanadī