Straight, to give warning of a severe punishment from Him & to give glad tidings to the believers who do righteous deeds, that they shall have a fair reward (i.e. Paradise). They shall abide [makithina] therein forever.
Imagine buying a beautiful house, on top of a beautiful hill, overlooking the blue ocean. Isn’t that going to be your most amazing property ever? But you know what happens after several years pass by? It’s not that beautiful anymore. Whatever possession or achievements we have right now, we will eventually get tired of it.
This Ayah says for the believers who do righteous deeds, their compensation is that they will be [makith]. [Makithna] means “to remain in wait/anticipation of something”. When we’re anticipating something, we’re always in a state of excitement because we’re about to enjoy something new [recall your first car purchase :)].
Allah s.w.t. says in this Ayah that there’s NEVER going to be a dull moment in Jannah. Perhaps some may have the idea that if everything goes exactly as what we want all the time in Jannah, then the excitement is not going to be there anymore. Nope! There will ALWAYS be anticipation and excitement. The inhabitants will live in Jannah where they are constantly looking forward to the next awesomeness. Subhanallah.
May Allah s.w.t. make us the people of Jannah. Ameen