The nature of man will never change, although it is subjected to conditions or states, such as separation of body and soul, the body can return to its physical element, but the soul which is the form of the body, and the source of it’s immanent activity with its faculties of intelligence and will will continue to exist independent of the body because they are spiritual. Yet since it is a created entity it is not unchangeable since it is not the source of its existence, and one of the features of a created entity is Potency and Act. It’s movement still exists, for God is still it’s prime mover. So the soul is like a big receptacle, constantly being filled by God, God pouring His goodness, knowledge into this receptacle. So the soul is undergoing a constant filling with God’s goodness, and truth, eternally, the Beatific Vision
God maintains the souls existence, and by doing so the soul exists eternally, and still remains a finite, created entity capable of enjoying God eternally. the body will again be united to the soul at the resurrection, and it will be spiritualized with the glory of the soul. Change still exists in the soul, but it is not physical change, the filling of the intellect, and the will is spiritual change, just as having a capacity to know, to the actual knowing is spiritual motion, and God is the prime mover. Time on earth is measured in physical change, and locomotion, physical movement, and the soul is extrinsically dependent on this change, as long as it is united to the physical body.