The fact is that God’s mercy extended to mankind had a beginning and it shall have an end. Prior to the fall of mankind there was no need for His mercy. At the end of the age of ages all shall be completely filled with the presence of God, and His mercy shall have overwhelmed all that stands in opposition to God, and again His mercy shall not be needed.
22 And He put all things under His feet, and gave Him to be head over all things to the church,
23 which is His body, the fullness of Him who fills all in all. (NKJV)
7 And when the thousand years are expired, Satan shall be loosed out of his prison,
8 And shall go out to deceive the nations which are in the four quarters of the earth, Gog and Magog, to gather them together to battle: the number of whom is as the sand of the sea.
9 And they went up on the breadth of the earth, and compassed the camp of the saints about, and the beloved city: and fire came down from God out of heaven, and devoured them.
10 And the devil that deceived them was cast into the lake of fire and brimstone, where the beast and the false prophet are, and shall be tormented day and night for ever and ever.
The return of Christ Jesus begins a millennium that has 1 thousand years that has no the open conflict.
As you may have read, I believe that the second death is remedial and not punitive. But if God removes all rebellion within the sin-nature, Death and Hades, nothing shall remain.
The war of Gog and Magog indicates the the sin-nature was suppressed, but not eliminated during the millennium of peace.
It is the Holy Spirit that enforces the will of the Father. The Father and Son chose those whom they will to be called and the time of that calling. Then the Holy Spirit comes to indwell at the appointed moment and seals us from the punishment that the Son has already paid on the cross. It all works in concert according to His mercy!