الرَّجْعِ (rain): Rain is a manifestation of the water cycle in the universe.  Starting from evaporation of the oceans and formation of the clouds in the sky that returns the rain over and over again. We do not benefit from water except when it descends and returns from the earth to the sky. Just in this case, water falls as fresh, valid for drinking and watering crops.

Allah (swt) Who has the power of returning the rain, has the power to re-create the man after death. Thus, when we read the following verses in Surah Adh-Dhariyat:

 {وَالذَّارِيَاتِ ذَرْوًا % فَالْحَامِلَاتِ وِقْرًا % فَالْجَارِيَاتِ يُسْرًا % فَالْمُقَسِّمَاتِ أَمْرًا % إِنَّمَا تُوعَدُونَ لَصَادِقٌ % وَإِنَّ الدِّينَ لَوَاقِعٌ}

(By those [winds] scattering [dust] dispersing % And those [clouds] carrying a load [of water] % And those [ships] sailing with ease % And those [angels] apportioning [each] matter, % Indeed, what you are promised is true. % And indeed, the recompense is to occur) (Adh-Dhariyat: 1-6)

We find that Allah (swt) made the whole water cycle in the universe from the starting point till its end a proof of His saying:

 إِنَّمَا تُوعَدُونَ لَصَادِقٌ

(Indeed, what you are promised is true.) (Adh-Dhariyat: 5)

That is, the resurrection is really true.

But, why the water cycle specifically? Scientists say that the water cycle is witnessed from all people from its starting point up to its end. So, the water that Allah (swt) has created in this universe does not increase nor decrease, rather, it is circulated.