The perfecting horizon—in the sense of “Our horizon is doing more than merely progressing—it’s perfecting.”—is the perfecting horizon of the present universe age, as described in paragraphs 48:8.3 and 117:2.1 of The Urantia Book (TUB).
Perfecting Horizons refers to the “expanding cosmic horizons” (TUB 104:2.3), expanding in the sense that “universal reality has an expanding and always relative meaning on the ascending and perfecting levels of the cosmos” (TUB 130:7.7).
To live a life with meaning—Why? Because: “If there is no survival of eternal values in the evolving soul of man, then mortal existence is without meaning, and life itself is a tragic illusion.” (TUB 111:3.7)