Why did Joseph Stalin decide that Russia had to industrialize rapidly?

Answer 1

He decided that it was a major advancement in the Soviet Union considering that Russia had always been behind the European countries of that time by a long shot. This had been very important especially with the changes that had to do with the NEP and new economic ideas of that time. Look further into detail about the NEP and policies like such.

Answer 2

Stalin recognized that Russia was a backward country in comparison to the western world and that unless it rapidly improved it's industry to become at least equal to the west, Russia would not survive. In a speechon February 4, 1931 he statd that Russia had been beaten in the past by the Mongols, Turks, Swedes Poles, Anglo-French and Japanese for being backward militarily, culturally, politically and industrially. He said:

"We have fallen behind the advanced countries by fifty to a hundred years. We must close that gap in ten years. Either we do this or we'll be crushed."