The term “atonement” is used over and over in the Old Testament to describe the purpose for and result of the Sinaitic (or Mosaic) sacrificial system. Many Christian theologians extrapolate the Old Testament concept into the New Testament setting and speak of the “atoning work of Christ on the cross.” This usage, however, obscures the very real difference between Old Testament atonement and New Testament expiation, propitiation and reconciliation. Atonement, in the Biblical sense, is a temporary covering up of sin, or guilt. A “stay of execution”, so to speak. Expiation means “to extinguish guilt incurred”. Propitiation is roughly the same, but with the additional dimension of appeasement of anger. Reconciliation means to “reestablish a close relationship” between two entities or concepts. Expiation and propitiation accurately describe what the death of Messiah did, while reconciliation, an accounting term, describes the resulting balance of our relationship with God. Cause and effect. Sin is paid for in full and permanently expunged from the record, God is appeased, and our relationship with Him is restored.
The Hebrew terms for “atonement” are variations from the root kaphar, which all carry the idea of “covering”; for example, covering a ship’s hull with bitumen to prevent leakage, or covering a stain in a hardwood floor with a rug. Orthodox Jewish males today cover their heads with kippot, the skullcaps or yarmulkes (Yiddish) that we have all seen. The “lid” of the Arc of the Covenant was called the kapporah, and it, too, is a covering. Atonement for sin, then, becomes a means of covering, or obscuring, it from sight, without actually expunging or removing it. The guilt remains, but God has provided a means of temporarily “sweeping it under the rug” pending permanent expungement by means of Messiah’s crucifixion.
Aside from references to the Jewish feast, the Day of Atonement, the words atone, or atonement appear seldom or not at all in most translations of the New Testament. In the Septuagint (LXX, the Greek version of the Old Testament used by Paul, translated, apparently, by 70 Jewish scholars in Elephantine, Egypt, in the 2nd Century, BC), the word “atonement” is rendered as hilasterion, because there apparently was not a Greek equivalent for “atonement”. Where the feast day is intended, the Greek hilasterion is thus also used in the New Testament for “atonement”, or even for “Mercy Seat”, referring to the covering of the Ark of the Covenant; otherwise, hilasterion is correctly translated as expiation or propitiation. Where the Greek katallagē is used, the proper translation is reconciliation.
Though most New Testament translations are generally okay in this respect, Christian writers and speakers continue to refer to phrases like, “the atoning blood of Christ”, which is a theological non-sequitur. Atonement is decidedly not what His crucifixion accomplished! The confusion arises because most Christians believe that the sacrifices were means of salvation under the Jewish Torah. But this is taught nowhere in scripture. Atonement by means of the sacrificial system is never said to make anybody “at one with Christ” or with God. Atonement is not “at-one-ment” as many have claimed. Salvation is permanent, whereas atonement is only temporary.
In discussing the superior sacrifice of Jesus, Heb 10:4 states that
Hebrews 10:4 (CJB)
 …it is impossible that the blood of bulls and goats should take away sins.
Many passages in the Tanach (Old Testament) also discuss the inadequacy of sacrifice in the presence of a sinful heart. For example
1 Samuel 15:22 (CJB)
 Sh’mu’el [Samuel]said,
“Does ADONAI take as much pleasure
in burnt offerings and sacrifices
as in obeying what ADONAI says?
Surely obeying is better than sacrifice,
and heeding orders than the fat of rams.
Psalms 40:7 (CJB)
7 Sacrifices and grain offerings you don’t want;
burnt offerings and sin offerings you don’t demand.
Instead, you have given me open ears;
Psalms 51:18 (CJB)
18 For you don’t want sacrifices, or I would give them;
you don’t take pleasure in burnt offerings.
Proverbs 15:8 (CJB)
 ADONAI detests the sacrifices of the wicked
but delights in the prayers of the upright.
Isaiah 1:11 (CJB)
 “Why are all those sacrifices
offered to me?” asks ADONAI.
“I’m fed up with burnt offerings of rams
and the fat of fattened animals!
I get no pleasure from the blood of bulls,
lambs and goats!
Jeremiah 6:20 (CJB)
 What do I care about incense from Sh’va [Sheba]
or sweet cane from a distant land?
Your burnt offerings are unacceptable,
your sacrifices don’t please me.”
Hosea 6:6 (CJB)
 For what I desire is mercy, not sacrifices,
knowledge of God more than burnt offerings.
Hosea 8:13 (CJB)
 They offer me sacrifices of flesh and eat them,
but ADONAI does not accept them.
Now he will recall their crimes and punish their sins—
they will return to Egypt.
Hosea 9:4 (CJB)
 They will not pour out wine offerings to ADONAI;
they will not be pleasing to him.
Their sacrifices will be for them like mourners’ food—
everyone eating it will be polluted.
For their food will be merely to satisfy their appetite;
it will not come into the house of ADONAI.
Why did God not want the sacrifices that He, Himself, had demanded? Just as we believe that baptism and the Lord’s Supper are a response of obedience by someone already saved, and useless to the unsaved, so were the sacrifices a response of obedience. Salvation then, as now, was “by grace through faith.” Sacrifice had no efficacy except to those who were already the recipients of God’s grace. The purpose of the sacrifices was to ritually “cover”, or hide from God’s eyes, the guilt of the sinner who, by his obedient sacrifice, was “making amends.”
But notice this: that every single one of the atoning sacrifices was for incidental, or unintentional, sin; in other words, for sins committed in ignorance, accidentally, or under duress. There was absolutely no means of sacrificial atonement for willful sin—except for God’s grace! On Yom Kippur, the “Day of Atonement” the Cohen HaGadol (high priest) would lay his hands on the forehead of the scapegoat, symbolically transferring to it all further, willful, sin. The goat would be led “outside the camp”, i.e., away from the people and out of God’s presence. Thus, the nation’s sin was allegorically returned to Azazel, the chief of demons.
When Jesus was crucified, He fulfilled not just the Passover sacrifice, but all other sacrifices, thus permanently expunging guilt for all unintentional sin. More than this, He also brought God’s full grace, by removing sin “from the camp” on the back of the scapegoat. The goat would be led outside the “camp”, never to be seen again!