in its full sense, duration of being without beginning, succession, or ending. Only God possesses the fullness of eternity, since only he always existed (no beginning), has no succession (no change), and will never end (no cessation). It is defined Catholic doctrine that God possesses the divine Being in a constant undivided now. His eternity is the perfect and simultaneous total possession of interminable life.
Rational creatures share in God's eternity, but only approximate it, by participation. Angels have a beginning, and they have a succession of past, present, and future, but they have no cessation since they are pure spirits that will never die or cease to be. Human beings likewise have a beginning and they have succession, but unlike the angels they will die in body, to be later resurrected, while the souls live on forever. In God's absolute power, however, angels and human souls could be deprived of existence. Their eternity depends on the goodness and will of God.