There is a prohibition against leaving a deceased person overnight without burial in the land of Israel. One of the reasons for this is that it causes impurity to the Holy Land, as is written, "And do not defile your land" (Deut. 21 23).

Impurity has no right to enter the land of Israel in the daytime, only at night….

The depth behind this law is as follows. The spirit of impurity has no right to enter the land of Israel in the daytime, only at night. Even at night the only way that it has permission to enter is if there is a corpse on the ground. Yet if there is no corpse then the spirit of impurity has no right to enter the Land. Even to rest its feet [figuratively] on the ground is prohibited. During the day, even if the land is full of corpses, spirit of impurity has absolutely no permission to enter.

There exists yet a more difficult negative force to contend with, namely the grasp of the External Forces. The Torah is very particular about this, as is stated, "His body you shall not leave…for you shall surely bury him on that day…and you shall not contaminate your land" (ibid.). We learn from this, that relative to the extreme defilement of the External Forces, the deceased in Israel is nearly pure. This is what is meant in the Zohar, which states, "The spirit of contamination has no rule over the Holy place [Israel]" (Teruma 141a).

The North…is the portal of the source of nourishment for the External Forces….

Nonetheless the impurity from the deceased (and its laws), is no worse than [that of the External Forces outside Israel]. Rather. the grasp of the External Forces outside of Israel is dependent upon the corpses being left unburied overnight. For the night is the time for the powers of the External Forces and all other negative aspects [to flex themselves]. All they need is a vessel to enter, attach themselves and claim their stake. This extra contamination causes much evil to the deceased. It brings punishment for the deceased, and in the heavens he is pestered about the presence of the extra contamination. Yet the mere defilement caused by death itself does not incur any punishment.

From the following, the Zohar brings another proof that the External Forces don't have any grasp in the Holy Land: [At night in the Holy Temple they didn't offer any sacrifices, rather they would ignite the remaining fats and innards of the sacrifices that were brought during the day.] The smoke of the burning remnants would ascend at an angle towards the North, where, which is the portal of the source of nourishment for the External Forces.

So long as his body is not buried, his soul is prevented from ascending….

Also, regarding the verse "His body you shall not leave hanging on the tree for you shall surely bury him on that day…and you shall not contaminate your land" (Deut. 21:23), the Zohar states:

If a deceased is left awaiting burial for twenty-four hours, including both day and night times, the limbs of the chariot are weakened. This also prevents the work of the Holy One Blessed Be He from being accomplished. This could come about if the Holy One Blessed Be He had caused his death with the plan of immediately reincarnating him [for his benefit] on that very day. And so long as his body is not buried, his soul is prevented from ascending before the Holy One Blessed Be He [for judgement], and can not be placed into a new body for reincarnation, for reincarnation is not possible until the burial of the first body. Therefore, the more the body awaits burial, the more the soul is pained. That is coupled by the forces of contamination attaching themselves to him, and defiling his body. Therefore it is incumbent upon us not to let a body go unburied for a night. For the forces of contamination abound a night and they fly around trying to find a body without a soul to inhabit and contaminate exceedingly.

From the above it seems that there are three types of blemishes that are caused by leaving a body unburied overnight:

  1. It blemishes the "Image of G‑d" [Tzelem] of that person

  2. It prevents the rectification of reincarnation

  3. It defiles and contaminates the land

These three are hinted at in the verse, "His body you shall not leave hanging on the tree for you shall surely bury [literally 'bury bury'] him on that day, for a hanging corpse is a curse of G‑d and you shall not contaminate your Land…" (Deut. 21:23)

He can return in a second reincarnation if he is buried on that day….

The message that G‑d is conveying is that he who is buried can be buried a second time, for he can return in a second reincarnation if he is buried on that day. As above, the soul can't be placed into a new body until the first one is buried. This is why the word "bury" is repeated in the verse.

The phrase "…for a hanging corpse is a curse of G‑d" conveys to us that a deceased who is not buried within 24 hours causes a weakening of the limbs of the chariot [i.e. the person] who was created in G‑d's image. This is from the contamination. That is the curse of G‑d. The final part of the verse, "and you shall not contaminate your Land", is best understood in its' simple explanation.