So the communist party only accepts the most advanced elements of the proletariat, people with the highest class consciousness. How does the party educate the rest of the population if it is that picky with who they let in?

I was told that the difference between the Bolsheviks and the Menscheviks was that the Menscheviks let anyone join, but the Bolsheviks only let people with advanced class consciousness join. How does that give popularity to a party if it is so exclusive?