‘Speak to the children of Israel, saying, If any one shall sin unwittingly, in any of the things which Yahweh has commanded not to be done, and shall do any one of them.'
Here we have a general introductory statement. It is a word to the children of Israel as a whole concerning the fact that ‘if anyone', whether priest, ruler or commoner, become aware of any way in which they have done what Yahweh has commanded not to be done, or if they find that they have failed to fulfil His requirements, then the purification for sin offering comes into play. It applies both for the one and the many, individual sin or community sin. For the one is the part of the whole. The sin in mind is ‘unwitting sin', sin caused by man's weakness and frailty, not sin done boldly and with a high hand. It covered sins that sprang from the weakness of the flesh (compare Numbers 15:27-29).
Sins resulting from human weakness, and the failure due to it, can be forgiven in such a way, but open defiance and deliberate thwarting of God's will, sins committed with a "high hand," cannot be dealt with through sacrifices. The latter included premeditated murder, the taking of a life which belonged to God (Exodus 21:12-14); idolatry, the setting aside of God for the worship of idols (Exodus 22:20, and especially in this context Deuteronomy 13:6-9; Deuteronomy 17:2-7); the taking in adultery of a man's wife who had been united with him by God, thus breaking the God-made tie (Leviticus 20:10); and being deeply involved with the occult (Exodus 22:18). In all these sins God was openly set at naught. Such a sinner was to be "cut off from among his people" (Numbers 15:30-31). This also included those who refused to listen to the requirements of the Law as taught by the priests and rulers of the people when speaking officially from God's Law, for they thus defied God whose Law it was and were to be put to death (compare Deuteronomy 17:12-13). So when David had committed adultery, which was a presumptuous sin, he could not just offer a sacrifice. Sacrifices were not available for that purpose. It was a direct sin against God and a far greater judgment resulted. All such sins were strictly punishable by death, and only direct dealings in penitence with God could divert such punishment.
The previous offerings have had in mind atonement, worship, adoration, thanksgiving and love. The purification for sin offering deals directly with the problem of specific sin and how it can be removed.
Interestingly this formula ‘if anyone ---' occurs in ritualistic formula elsewhere, including those dating from 2nd millennium BC.