How can semen be pure, when ghusl is obligatory after it, while urine only requires caution?

The sayings of the jurists varied regarding semen, oscillating between purity and impurity. The Almighty's saying, "from a despised water," does not mean that semen is impure, for in language, "despised" means weak and lowly. The evidence for the obligation of ghusl (ritual bath) due to semen is not because it is impure, for if that were the case, ghusl would be obligatory for urine and other impurities. The wisdom behind ghusl from semen lies in the fact that it exits from the entire body and causes heaviness and sluggishness, and ghusl revitalizes the body and spirit, and restores strength after intercourse.