Which was an important change for the Roman Empire during the reign of Constantine?

There were many important changes under the reign of Constantine. But the biggest one of them all is converting Rome to Christianity. Why? For hundreds of years, the Romans killed millions of Jews and Christians alike, proclaiming that there is no 'one' God. When Constantine converted to Christianity, he shocked everyone. And since their emperor converted to another religion, they were forced to convert too. Christianity became Rome's official religion until its end.