Thomas Aquinas, Compendium of Theology

Man's consummation consists in the attainment of his last end, which is perfect beatitude or happiness, and this consists in the vision of God, as was demonstrated above. The beatific vision entails immutability in the intellect and will. As regards the intellect, its questing ceases when at last it comes to the first cause, in which all truth can be known. The will's variability ceases, too; for, when it reaches its last end, in which is contained the fullness of all goodness, it finds nothing further to be desired. The will is subject to change because it craves what it does not possess. Clearly, therefore, the final consummation of man consists in perfect repose or unchangeableness as regards both intellect and will.