﴿28﴾ وَهُوَ الَّذِي يُنَزِّلُ الْغَيْثَ مِنْ بَعْدِ مَا قَنَطُوا وَيَنْشُرُ رَحْمَتَهُ وَهُوَ الْوَلِيُّ الْحَمِيدُ
28. And He it is Who sends down the rain after they have despaired and spreads His Mercy. And He is the Protector, Worthy of all praise.
Rain is a manifestation of Divine Mercy and decrease in the amount of rain impedes man’s disobedience. The Arabic word ghayth is applied to fruitful rain whereas the word matar designates any kind of rain, fruitful or harmful, as it is reflected elsewhere (25:40) in the Holy Qur'an: “And indeed they have passed by the town [of Prophet Lot (AS)] on which was rained the evil rain.”
The blessed Verse in question says that one of the Signs of Divine Bounty and Mercy is that you were desperate at the time of famine, but He sent down rain for you and distributed His Mercy so that your provision may be enlarged and your trees and crops may thrive. He is you Friend whom you are supposed to obey in return for His Bounties and you are supposed to praise your Lord.