Assess how important purges were in allowing Stalin to retain control of Russia 1930-1940?

The command word in this question is 'assess'. That means they want you to compare the purges with other developments occurring throughout the period and reach a final judgement: for example, arguing the purges were more important than cultural factors and the cult of personality because they removed potential opponents of Stalin and centralised the Communist Party. It is very important that you have good background knowledge to answer this question.A potential introduction to a top-mark answer may be: "Stalin's purges were the most important factor in allowing Stalin to retain control of Russia. This is because they enabled Stalin to remove opponents (such as Zinoviev and Kamenev in August 1936) and terrorise people, thereby allowing him to implement his other policies and streamline the Communist Party around him. Other factors, such as cultural changes, the cult of personality and economic policy were less important because they were only implemented as a result of the control Stalin had amassed during the purges. It would be wrong to say that Stalin gained complete control only as a result of the purges, but they were clearly the cornerstone of his efforts."