As a Christian humanist and someone profoundly influenced by the Greek philosopher Plato, Milton had a certain contemptus mundi, a negative attitude towards the things of this world. For him, as for his illustrious forebear, life on earth represented but a poor copy of a world of timeless archetypes in which the truth resided.

One of the least appealing aspects of our worldly existence is time, to which all are subject and which Milton regards as an impediment to happiness. That's why Milton wishes that time would fly, that it would run its course as quickly as possible and, in doing so, consume all that's negative in the world before destroying itself.

Only once this has happened will humans be truly happy. Heaven in all its glory will come down to earth, an earth expunged of all the negative features of creaturely existence: “Death, and Chance, and thee O Time.”

Notice how Milton capitalizes these abstract nouns. This is to indicate that they are forces in their own right, powerful forces that exercise such a profound impact upon people's lives. It's almost as if they have human qualities.

Milton envisages a glorious fantasy in which the earth, no longer subject to death, time, and chance, will be a truly happy place in which “Truth, and Peace, and Love”—again, note the use of capitalization—shine about “the supreme Throne.” In other words, all the things that were negative about our world—such as time—will be replaced by positive entities oriented towards God.