If we want to go to Heaven, we should know the law in Heaven and respect it by keeping our body, speech and mind clean. Body means we purify our body by avoiding eating the dirty meat of animals. This is the most important. Heavenly beings are so kind that they cannot bear to see us eating meat and killing cows and pigs. They don't like to have that kind of people in heaven. In our speech, we do not talk about right and wrong, or garbage or bad things. Mind means that we think about higher worlds, great powers, the power of Bodhisattva and the noble manners, and do not want to do bad things or immoral things. Thus by keeping our body, speech and mind clean, we will be able to go to Heaven.
Why do we need to learn from an enlightened master? Because we also don't know if our body, speech and mind are clean or not. Therefore, we learn from a very pure person, since that kind of person has already learned well and cleansed his body, speech and mind. If we come and learn from him, he will remind us where we are not clean and tell us how to go to Heaven and what the heavenly law is like.