Or... Jesus meant that the atonement He was sent to perform was finished; not that the effect of the atonement had been fully applied to all those who would eventually be regenerated and persevere to the end..
The atonement that was completed for all.
It needs nothing added to save everyone and anyone who wishes to believe in Christ.
Its stands completed forever and will always be so.
Yet,, even the unbeliever will not have his sins mentioned at the final judgement.
The atonement eliminated the condemnation that comes from being fallen.
The unbeliever will not hear one personal sin being mentioned when he is brought before the Lord.
The devil, who deceived them, was cast into the lake of fire and brimstone
where the beast and the false prophet are. And they will be tormented day
and night forever and ever.
Then I saw a great white throne and Him who sat on it, from whose face the
earth and the heaven fled away. And there was found no place for them.
And I saw the dead, small and great, standing before God, and books were opened.
And another book was opened, which is the Book of Life. And the dead were judged
according to their works, by the things which were written in the books. The sea gave
up the dead who were in it, and Death and Hades delivered up the dead who were
in them. And they were judged, each one according to his works. Then Death and
Hades were cast into the lake of fire. This is the second death. "
Revelation 20:10-14
Unbelievers will not be condemned according to their sins.
For their sins were already judged on the Cross. The atonement was completed forever!
But, unbelievers will be judged according to their works.
Why?
One work will be sought for in the book and not found.
Then they said to Him, “What shall we do, that we may work the works of God?”
Jesus answered and said to them,
“This is the work of God, that you believe in Him whom He sent.” John 6:28-29
Not by works,
But one single work.
One specific single work required of God.