Atonement of your sins means the forgiveness of them, meaning having the blood of Christ sprinkling on you
Back in the OT, the priests would sprinkle the blood offering of atonement on the people of God.
This was never done for those not of God.
1 Peter 1
Peter, an apostle of Jesus Christ,
To the [
a]pilgrims of the Dispersion in Pontus, Galatia, Cappadocia, Asia, and Bithynia,
2 elect according to the foreknowledge of God the Father, in sanctification of the Spirit, for obedience and sprinkling of the blood of Jesus Christ:
Grace to you and peace be multiplied.
A Heavenly Inheritance
3 Blessed
be the God and Father of our Lord Jesus Christ, who according to His abundant mercy has begotten us again to a living hope through the resurrection of Jesus Christ from the dead, 4 to an inheritance [
b]incorruptible and undefiled and that does not fade away, reserved in heaven for you, 5 who are kept by the power of God through faith for salvation ready to be revealed in the last time.
6 In this you greatly rejoice, though now for a little while, if need be, you have been [
c]grieved by various trials, 7 that the genuineness of your faith,
being much more precious than gold that perishes, though it is tested by fire, may be found to praise, honor, and glory at the revelation of Jesus Christ, 8 whom having not [
d]seen you love. Though now you do not see
Him, yet believing, you rejoice with joy inexpressible and full of glory, 9 receiving the end of your faith—the salvation of
your souls.
Unbelievers do not have their sins forgiven, they die in their sin.
And that means hellfire waits them.
Atonement must necessarily always be limited to the believing otherwise you're going way beyond scripture and are a universalist.
Exodus 24, the BLOOD of the Covenant
3 So Moses came and told the people all the words of the Lord and all the [
a]judgments. And all the people answered with one voice and said, “All the words which the Lord has said we will do.” 4 And Moses wrote all the words of the Lord. And he rose early in the morning, and built an altar at the foot of the mountain, and twelve pillars according to the twelve tribes of Israel. 5 Then he sent young men of the children of Israel, who offered burnt offerings and sacrificed peace offerings of oxen to the Lord. 6 And Moses took half the blood and put
it in basins, and half the blood he sprinkled on the altar. 7 Then he took the Book of the Covenant and read in the hearing of the people. And they said, “All that the Lord has said we will do, and be obedient.” 8
And Moses took the blood, sprinkled it on the people, and said, “This is the blood of the covenant which the Lord has made with you according to all these words.”
Hebrews 12
22 But you have come to Mount Zion and to the city of the living God, the heavenly Jerusalem, to an innumerable company of angels, 23 to the [
j]general assembly and church of the firstborn
who are registered in heaven, to God the Judge of all, to the spirits of just men made perfect, 24 to Jesus the Mediator of the new covenant, and to the blood of sprinkling that speaks better things than
that of Abel.
If you are not one of Christ's sheep then you have no part in God's New Covenant.