When god first created the world, there was no desert. The whole world was filled with fertile lands full of beautiful gardens. God created man in order to maintain the world. He said to man, "Every time you commit a sin, there will be a peck of sand falling on the ground". Man thought, "What harm will a peck of sand do? let me live as I please". He started committing wicked sins and pecks of sand started falling on the ground. Still man continued sinning. And the effect is that to-day there are many deserts a around us. 
As you sow, so you reap. 