We can agree that the law of first thermodynamic true. Then matter and energy also cannot be created or destroyed. Something that cannot be created cannot have a point in which it was created, therefore doesn’t have a start. If matter and energy is semptiternal, the universe itself is senpiternal(the universe is defined as the totality of everything that exists). Thus a sempiternal universe would contradict the existence of a classical theistic God who created the universe(in which God didn’t) from nothing(creatio ex nihilo), that would be the whole concept of a classical theistic God.