What is the purpose of the great purges of the 50s and 60s?

The purges were public spectacles and warnings to the people.... After the purges, everyone was well reminded that people who made political comments against the Party or its platforms would experience the same fate, maybe not is a public way, but they would experience it none-the-less.

The great purges involving thousands of people, with public trials of traitors and thought-criminals who made abject confession of their crimes and were afterwards executed, were special show-pieces not occurring oftener than once in a couple of years.