Shalom and thank you for your question! You have found sources regarding the concept of atonement that date it back about five hundred years. Atonement means performing an action to rectify a misdeed, in other words, it has to do with repenting and returning to G-d and his ways. The instruction to return to G-d, often translated as ‘repentance’, is mentioned in Deuteronomy 30:2 “And you shall return unto the L-rd your G-d…
The concept of ‘atonement’ comes even earlier than that in the book of Exodus, where the Sin of the Golden Calf takes place. The atonement for that sin was, surprisingly, the building of the sanctuary, Mishkan, in the desert. The Mishkan was the precedent for the Holy Temple that was to be built in Jerusalem. It was the place where sacrifices were offered up to G-d, through the services of the High Priest Aharon and his sons.
To understand how the building of the sanctuary could atone for the above-mentioned sin, we need to look at the Hebrew word the Bible uses. Chet in Hebrew is related to the word ‘lack’. The Jewish people in the desert were lacking somewhat in faith, even though they had so recently witnessed the revelation of G-d at the giving of the Torah. Commentaries discuss the reasons they were ‘pushed off the edge’ to go to the extent of idol worship, and there are many things that could be said in their defense. Nevertheless, the act was committed, and needed to be rectified. Idol worship means straying from the loving relationship that we are to have with G-d, who is called ‘Our Father, Our King,’ in the prayers.
The word for sanctuary in Hebrew, Mishkan, comes from the root ‘dwell’. The Divine Presence dwelled with the Jewish people in the sanctuary. If the King is scheduled to visit your local town hall regularly, not only will you keep the place clean, keep the best wine and refreshments on hand, but you will regard that town hall as a very special place, and feel rather self conscious if you make a comment there that would not be complimentary to the King, or even a subject of the King. How much more so when we are talking about G-d Himself, not a mortal King. The Jewish people’s ‘sin’ with the Golden Calf expressed a lack, and G-d came to fulfil that lack by investing the Divine Presence into that material structure. This can only work when it is done according to the Divine instructions. The sanctuary was built with the material possessions of the Jewish people in the desert. In this way, they demonstrated their acknowledgement of the absolute unity of G-d , by offering up their own possessions in the place designated to serve Him. We must serve G-d at all times and in all places, by behaving according to His instructions as laid out in the commandments of the Torah and the Seven Noahide laws for non-Jews, but the sanctuary and the Temple were designated for offering up sacrifices and gaining inspiration for this purpose.
The Torah lays out clear instructions for carrying out the commandments, and results for not carrying them out. Some of those results have to do with ‘punishments’ meted out by Heaven, like the Biblical leprosy which is not related to the disease known as leprosy in our day. It was a supernatural phenomenon which in Biblical times would happen to a person who was guilty of slander, and the purification process involved the ministering of the priests, or Cohanim. Since the Jews were exiled after the destruction of the Second Temple, the Divine Presence no longer manifested itself in this supernatural way. We had to search for G-d in our inner Temples.
The Oral law handed down by Moses and his successors together with the written law (Tractate Ethics of the Fathers, 1:1,), as expressed in the Talmud and the Codifiers who base themselves on the Talmud, provides us with instructions as to how to atone for our sins today. We must firstly acknowledge our sin, we must regret it, and resolve to act differently in the future. This is an inner process that necessitates honesty and self- awareness. Jethro advised Moses in the book of Exodus, to set up a system of judges to be assigned to progressively smaller groups of the people, so that there would be knowledgeable people to address the spiritual needs of the entire nation, since one man alone could not do so without becoming exceedingly ‘burnt out.’ In the same way, the above-mentioned tractate ‘Ethics of the Fathers’, counsels us, ‘Make for yourself a Rabbi and acquire for yourself a friend.’
In other words, we need to have spiritual guides and friends who are a good influence to help us along in our personal quest for bridging the gap between our natural desires and our spiritual destination, namely to repair the relationship with G-d that has been damaged by our lack of faith, and/or misdeeds.
We need to be ‘At one’ with G-d, and this is atonement.
