Eternity means for ever. It is very difficult for the intellect to grasp the concept of eternity simply because it is itself transient. Eternity means without aging or growing old, without change. This is an inherent characteristic of God and the Divine. The Primordial Spiritual and the Spiritual Realms are also eternal. Even the Animistic realm is. It is a characteristic of those realms, which are mobile in themselves.
The creatures that are permitted to live in these realms are also eternal. It is only in the material world do the concept of change come in. Here, there is always a coming into being, development, growth, maturation and disintegration. Such transformations are not to be found in the Spiritual Realms.
These realms are able to receive a constant stream of power from the Holy Spirit, which prevents them from aging. The real reason then for this characteristic is the proximity to the Will of God whereby they can always uninterruptedly receive of the power of the Holy Spirit. Material creation does not have this access simply because it is too far away.
The immense distance from the Creator prevents a direct access to this quickening power of God. To make matters worse, human beings, due to the subjection of our wills to the darkness have dragged subsequent creation further downwards thereby altogether precluding any possibility of the Light reaching the World of Matter. This is because through the specific quality of our intuitive perceptions, we are meant to be the mediators for the flow of this quickening Power to the earth and indeed the entire Subsequent Creation.