"All have sinned, all come short of the glory of God, but they are justified for nothing by His grace through the ransom provided in Christ Jesus, whom God put forward as the means of propitiation by His blood, to be received by faith" (Romans 3:23-24).
The Term "Propitiation"
The Greek word (hilasterion) is derived from a verb which in pagan writers and inscriptions has two meanings:
(a) "to placate" a man or a god;
(b) "to expiate" a sin, i.e. to perform an act (such as the payment of a fine or the offering of a sacrifice) by which its guilt is annulled.
The former meaning is overwhelmingly the more common. In the Septuagint, on the other hand, the meaning (a) is practically unknown where God is the object, and the meaning (b) is found in scores of passages. Thus the biblical sense of the verb is "to perform an act whereby guilt or defilement is removed." The idea underlying it is characteristic of primitive religion. The ancients felt that if a taboo was infringed, the person or thing involved became unclean, defiled or profane. The condition of defilement might be removed by the performance of the appropriate act: it might be washing with water, or sprinkling with blood, or simply the forfeiture of some valuable object to the deity concerned with the taboo. Such acts were felt to have the value, so to speak, of a disinfectant. Thus in the Old Testament a whole range of ritual actions are prescribed for disinfecting the priest, the altar, or the people from various forms of defilement, ritual or moral. Our versions in such cases use the phrase "to make propitiation"; but the more proper translation would be "to make expiation". This meaning holds good wherever the subject of the verb is a man. But, as religious thought advanced, it came to be felt that, where the defilement was moral, God alone could annul it; and so the same verb is used with God as subject in the sense "to forgive".*
In accordance with biblical usage, therefore, the substantive (hilasterion) would mean, not propitiation, but "a means by which guilt is annulled": if a man is the agent, the meaning would be "a means of expiation"; if God, "a means by which sin is forgiven". Biblical usage is determinative for Paul. The rendering "propitiation" is therefore misleading, for it suggests the placating of an angry God, and although this would be in accord with pagan usage, it is foreign to biblical usage. In the present passage it is God who puts forward the means whereby the guilt of sin is removed, by sending Christ. The sending of Christ, therefore, is the divine method of forgiveness. This brings the teaching of the present passage into exact harmony with that of v. 8-9.
* The full evidence for all this is given in my book, The Bible and the Greeks, pp. 82-95, where I have examined, I believe, every occurrence of the verb in the Septuagint.
From The Epistle of Paul to the Romans, Fontana Books (1959), pp. 78-79.