God presented Christ as a sacrifice of atonement (Greek: hilastḗrion), through the shedding of his blood—to be received by faith. He did this to demonstrate his righteousness, because in his forbearance he had left the sins committed beforehand unpunished... -Rom 3:25 (NIV)
And not only so, but we also joy in God through our Lord Jesus Christ, by whom we have now received the atonement (Greekk: katallagḗ). -Rom 5:11 (KJV)
We need to be conscious and careful of the words we use. The KJV uses "atonement" only once (Romans 5), but Christ is not offering an "atonement." The better word would be "reconciliation" (translated this way in the three other instances of the Greek word in the KJV). The atonement was a covering of the sins of the redeemed nation of Israel. The work of Christ is complete. We do not have nor need atonement.
if, being enemies, we have been reconciled to God through the death of His Son, much more, having been reconciled, we shall be saved in his life [resurrection]. And not only [so], but we are also boasting in God, through our Lord Jesus Christ, through whom now we did receive the reconciliation. -Rom 3:25 (Young'd Literal)
The Greek word "hilastḗrion" used here is only used one other place in the Greek scriptures: Hebrews 9:5 where it is translated "mercy seat." We see the argument Paul is making to Hebrews (Jews) in regard to the finished work of the Savior.
These preparations having thus been made, the priests go continually into the outer tent, performing their ritual duties; but into the second only the high priest goes, and he but once a year, and not without taking blood which he offers for himself and for the errors of the people. By this the Holy Spirit indicates that the way into the sanctuary is not yet opened as long as the outer tent s still standing (which is symbolic for the present age). According to this arrangement, gifts and sacrifices are offered which cannot perfect the conscience of the worshiper, but deal only with food and drink and various ablutions, regulations for the body imposed until the time of reformation. But when Christ appeared as a high priest of the good things that have come, then through the greater and more perfect tent (not made with hands, that is, not of this creation) he entered once for all into the Holy Place, taking not the blood of goats and calves but his own blood, thus securing an eternal redemption. For if the sprinkling of defiled persons with the blood of goats and bulls and with the ashes of a heifer sanctifies for the purification of the flesh, how much more shall the blood of Christ, who through the eternal Spirit offered himself without blemish to God, purify your conscience from dead works to serve the living God. -Heb 9:6-14 (RSV)
For the life of the flesh is in the blood, and I have given it to you upon the altar to make atonement for your souls; for it is the blood that makes atonement for the soul.’ Therefore I said to the children of Israel, ‘No one among you shall eat blood, nor shall any stranger who dwells among you eat blood.’ -Lev 17:11-12
Therefore I judge that we should not trouble those from among the Gentiles who are turning to God, but that we write to them to abstain from things polluted by idols, from sexual immorality, from things strangled, and from blood. -Acts 15:19-20
And the Lord said to Moses and Aaron, “This is the ordinance of the Passover: No foreigner shall eat it. But every man’s servant who is bought for money, when you have circumcised him, then he may eat it... And when a stranger dwells with you and wants to keep the Passover to the Lord, let all his males be circumcised, and then let him come near and keep it; and he shall be as a native of the land. For no uncircumcised person shall eat it. -Ex 11:43-44; 12:48
God is no longer imputing sins to anyone. "God was in Christ reconciling the world to Himself, not imputing their trespasses to them, and has committed to us the word of reconciliation."
The world's sins are already paid . We call on people to be reconciled to God because he has already been reconciled to them. We moved from "God is a just judge, And God is angry with the wicked every day" (Ps 7:11) to God still being just but now that "He might be just and the justifier of the one who has faith in Jesus" (Rom 3:26).
The Reformed doctrine of "limited atonement" is a double error. When coupled with mythology of a God torturing people with fire for rejecting a free gift, we have horribly distorted both the loving character of God and the nature of what Christ fully accomplished.