(Urgent) The law stipulates the future, and the judge judges the past. What does that mean? What angles should we analyze from jurisprudence?

The law stipulates the future, which means that the law generally restricts the legal acts after the law is enacted, and generally has no legal binding force on the previous acts, that is, it emphasizes a retrospective issue. Under normal circumstances, judges make judgments for the past and ignore civil cases. Therefore, since making a judgment in a trial must be an objective act that has happened, then a criminal case must also be a criminal act that has been committed, right? Therefore, this is a legal treatment of the legality of past cases.