Answer: 1) make them enter their institutions (not necessarily Communist party) and like that to control them (their lives), 2) to discredit other non-Communist institutions (non-Communist parties, church etc.), 3) trying to infiltrate to other non-Communist institutions and organizations to get some loyal people there and like that to get influence there (army, church, schools, universities, academies, in science, among writers and intellectuals), 4) propaganda.
Explanation: Communism as well as fascism and other ideologies tried to win people in the time of secularization. During the 19th century European population was loosing their faith in church or Scripture and was looking for something different. There were many who experienced seriour existential or religious crisis. Science was winning hearts of people and credibility. There was a faith in a capacity of science to make people happy and capable to fulfil their lives ....it was Marx who capitalized on that feeling. Marx and Lenin and Communists were able to convince many people that society can be sciencifically transformed (Marxist or Marxist-Leninist ideology) and create a society where everyone would be happy.