Adam Clarke on Revelation 2:28

And I will give him the morning star - He shall have the brightest and most glorious empire, next to that of Christ himself. And it is certain that the Roman empire under Constantine the Great was the brightest emblem of the latter day glory which has ever yet been exhibited to the world. It is well known that sun, moon, and stars are emblems, in prophetic language, of empires, kingdoms, and states. And as the morning star is that which immediately precedes the rising of the sun, it probably here intends an empire which should usher in the universal sway of the kingdom of Christ.

Ever since the time of Constantine the light of true religion has been increasingly diffused, and is shining more and more unto the perfect day.