Here’s the bad news/good news about that saying:
You are NOT getting into heaven UNLESS you are a saint.
Purgatory is not a second chance for Catholics. At death you are hopefully going to heaven because the alternative is just hell. But for most on the path to heaven, there will be a cleansing of our un-heavenly desires. WHATEVER THIS IS (and it is not exactly clear) that is what purgatory is.
Here’s the good news: Despite what most people think and what our statues might depict, saints are not perfect people. They are human beings. From Peter, to Jerome, to John Paul II, saints are people who erred in many aspects of their lives, were in ample need of the sacrament of confession and like Saint Paul said, “I do not understand what I do. For what I want to do I do not do, but what I hate I do. And if I do what I do not want to do, I agree that the law is good. As it is, it is no longer I myself who do it, but it is sin living in me. For I know that good itself does not dwell in me, that is, in my sinful nature. For I have the desire to do what is good, but I cannot carry it out. For I do not do the good I want to do, but the evil I do not want to do—this I keep on doing. Now if I do what I do not want to do, it is no longer I who do it, but it is sin living in me that does it.” Romans 7:15-20.
The difference between saints and non-saints? Saints are faithful. Do you want to begin to understand what it is to be faithful? Think of the most faithful friend you ever had - or what you would like in a most faithful friend. Then start by being that to God and you are well on your way to sainthood.