The answer
In order to truly understand the Kingdom of Christ, we must first know what are the First and Second Resurrections, and what are the first and second deaths?
The First Death is the death of sin (Eph. 5:11).
The First Resurrection is the life of repentance (John 5:24-25).
The Second Death is the torment of Gehenna, which comes as a result of man’s indulgence in sin without repentance (Rev. 20:12-14).
The Second Resurrection is either the resurrection unto life, or the resurrection unto condemnation, in the coming of the Son of Man (John 5:28-29).
This means that Christ’s Kingdom is spiritual, and without end. It began on the Cross, and continues unto eternity, without end. This negates the notion that the Kingdom is determined by a timely duration, with a beginning and an end, as we just said.
His Holiness Pope Tawadros II
Pope Tawadros II, My Faith: A Series of Dialogues on the Creed (Coptic Orthodox Patriarchate, 2014), 126–127.

