Stalin promoted socialist realism in order to (a)show soviet life positively and promote hope in a communist future. (b)root out counterrevolutionaries and send them away to the gulags. (c)show soviet life in a realistic light and celebrate communist victories. (d)convince people outside of the soviet union of the value of communist virtues.

I believe the answer is: show Soviet life positively and promote hope in a Communist future.

Stalin aimed to create a utopian society where there is no social class that exists among people and people could have an exactly equal distribution of wealth.
But along the way, this system fail to provide incentives for people to work hard and achieve more things, which eventually destroy their economy.