Eternity

Wikipedia, abbreviated:
Eternity: It denotes the quality and state of a being/mind or substance that is absolutely not subject to time, that is, having no beginning, continuation, or end to its existence. Eternity also implies the infinite continuation or repetition of a given existence in time. Eternity is a duration that has no cycle.

Gennady, introduction: Nothing can exist outside of God, as this contradicts the concept of the word GOD. Therefore, all eternity is within God. And it is encompassed by the Holy Spirit, by Whom all eternity is governed. The Holy Spirit is emitted—sent—by the Heavenly Father and His Son. Eternity and infinity of all existence are constantly encompassed by the Holy Spirit. We all depart into eternity for various reasons: illness or otherwise. One of my readers responded to this: "Dying is not scary, the process of dying is terrible," but this does not apply to believers. Faith in God helps us in this!

What is eternity? Author: Valery Dukhanin
It's probably difficult to immediately understand what eternity is. After all, we live in time and often see things begin and then end, and therefore are not eternal. But there is the Lord God, Who is incomparably superior to our created world, independent of time; His being has no beginning and will never have an end. He willed that the rational beings He created also partake of eternity. Incidentally, in our world, something that has neither beginning nor end—the circle—is a symbol of eternity, and in Christianity, it is a symbol of eternity.

At the same time, it is necessary to distinguish between the eternity that belongs to God alone and the eternity bestowed upon created beings. God has always existed, and His being has no beginning, and since God is beyond time, His being will never end. That is, His eternity is uncreated, belonging only to Him. But the eternity granted to created beings is of a different order: all created things have a beginning; once upon a time, nothing created existed. In this sense, we are not eternal, or rather, not beginningless.

Of course, beings of the spiritual world—angels—and human souls will never disappear, but only by the gift of the Creator, not by their own self-sufficiency. In other words, God imbued the spiritual nature of created beings—angels and human souls—with the gift of immortality; therefore, the existence of the spiritual-created world, once begun, will never end.

In the Revelation of John the Theologian concerning the final destinies of the earthly world, it is stated that with the Second Coming of Christ and the advent of His gracious, eternal Kingdom, time will no longer exist (Rev. 10:6). The life of the age to come is a mystery that we cannot fully comprehend now. But we can know that it is in eternity that the existence of created beings will be revealed in the fullness of its calling. Eternity is not an infinite duration of time, but a new existence, unconstrained by earthly, spatio-temporal boundaries. To understand this, let us note that the prelude to this eternity is already approaching for people, manifesting His help to others through their prayers anywhere in the world, and that no matter how many people simultaneously pray to the saint, He hears each one's sincere request, something that would be impossible under earthly limitations. However, we can only truly comprehend eternity by entering it. May God grant that a good fate awaits each of us in eternity.

And further:
"God is eternal. God's existence is timeless, for time is only a form
offinite and changeable existence. (Time is considered the "fourth"
dimension in relativistic physics. According to modern cosmology,
space and time are not infinite. They appeared and will disappear
along with the world.) For God, there is neither past nor future, but
only the present. "In the beginning You (Lord) laid the foundation of
the earth, and the heavens are the work of Your hands. They will
perish, but You will remain. They will all wax old like a garment, and
like a vesture You will change them, and they will be changed. But You
remain the same, and Your years will have no end" (Psalm 102:26-28).
Some Holy Fathers point out the difference between the concepts
of "eternity" and "immortality."

Eternity is vitality, having neither beginning nor end. "The concept
of eternity can be applied only to the one, beginningless Divine nature,
in which everything is always the same and in the same form. The concept
of immortality can be ascribedto that which is brought into being and
does not die, such as angels a nd the human soul...The eternal in the
proper sense belongs only tothe divine essence" (St. Isidore of Pelusium).
In this regard, even more expressive is "the eternal God."
Bishop Alexander Mileant.