At the end of the parasha, the Torah brings the following case: "If a person sins and acts deceitfully against Hashem, by denying his friend’s (claim) regarding an article that was deposited by him…" (Vayikra 5:21).
The opening words of the pasuk imply that the sin is within the realm of "between man – and G-d." However, the specific description is of a sin between man and man. Chazal sensed the seeming contradiction. We will bring Rabbi Akiva’s explanation in Midrash Halacha, cited by Rashi.
"When someone gives another a loan, or does a business deal, it is done with witnesses and a document. Therefore when one denies the action – he denies the validity of the witnesses or document. But when one deposits something with his friend, he does not want many people to know about it – only the third party (=Hashem). Hence when one denies the deposit, he is also denying the third party."
According to the Midrash, when one deposits an object, we are most probably talking about a friend whom the depositor trusts. The depositor doesn’t want other people to know, as this heightens the risk of theft or for other reasons. Therefore when the guardian denies that the act took place, he abuses the situation where there are no other witnesses other than G-d. Therefore the denial of the deposit is simultaneously a denial of G-d, and not just an abuse of their friendship.
This seems to be the reason that the Torah uses the word "me’ila (taking deceitfully)" even though this is usually used only in the context of taking from sanctified donations. The word me’ila comes from the root word me’il (cloak). Similarly the word begida (unfaithfulness) is related to the word beged (garment).
The cloak and garment are used to protect oneself. One also shares his clothes with friends. Hence any unfaithfulness by close friends or family is described as me’ila or begida – a misuse of the close bond that was meant to protect oneself. Similarly his friend (amit) becomes his opponent (immut), as the Ibn Ezra points out.
A person who does such a sin is obligated to bring a sin offering over and above returning the stolen article. The Mishna brings an interesting halacha: "If one brought the stolen article but not the sin offering, he fulfilled his obligation. If he brought the sin offering but did not bring the stolen article, he does not fulfill his obligation" (Bava Kama 110a). In other words, one cannot bring the sin offering to sort out the sin "between man and G-d" and only afterwards fix the injustice between man and man.
Rabbi Elazar Ben Azarya taught that Yom Kippur atones for all sins other than those between man and man, which require appeasing the victim (Mishna, Yoma 8:9). The simple explanation is that on Yom Kippur one can only ask forgiveness from Hashem regarding sins between man and Hashem, but sins between people need a request of forgiveness. Based on our words above, we can explain that Rabbi Elazar stated a novel idea. Even regarding sins "between man and man" there is an element of "between man and G-d." One cannot gain atonement from G-d for even this element before he has asked forgiveness from his friend.
Let us pray that we are all able to remain faithful even to those closest to us and not sin against them, or Hashem.