To revitalize is to restore something to life or give it new life. Revitalizing adds newsness and strength.
Since vital things are alive, strong, and flourishing, when something gets revitalized, it is returned to health or life. A good night's sleep will revitalize you — so will eating a healthy meal. If a rundown building is purchased and then spiffed up, it's being revitalized. A new paint job could revitalize a room. A sick person is revitalized by medicine. In all cases, when something is revitalized, it has been restored to a better state.