Gate of Reincarnations
Rabbi Yitzchak Luria
Four Souls, One Person
Chapter Five, Section 2

We will now further clarify the subject that we began previously. The verse says, "…Visit the sins of the fathers on the children for three and four (generations)" (Shemot 20:5). This means that up to three reincarnating Nefashot can reincarnate with a new Nefesh together in one body at birth. This makes for a total of four Nefashot at one time. This is the secret of "four."

It is also the secret of the verse "…two or three times with a man" (Iyov 33:29). Three Nefashot are able to reincarnate with one "man", who is this new Nefesh. However, it is not possible for more than this to reincarnate at one time. However, less than this amount is possible.

It is possible that one Nefesh can reincarnate alone in a body; or one reincarnated Nefesh with a new Nefesh. Or, two reincarnated Nefashot by themselves can go into one body; or two reincarnated Nefashot with a new one; or three reincarnated Nefashot by themselves; or three reincarnated souls with a new one. However, more than this is not possible within one body.

Know that those that are reincarnating together in a single body must all be of a single "root". This is the esoteric meaning of the verse
"…he shall redeem the property of his brother" (VaYikra 25:25).

As a result, even though the first time gilgul has not committed any of the sins of the previous gilgulim, he will still have to cleanse the blemish and stench that resulted from their earlier sins. This will be the case if he is from a more internal [primary] level than the others, such as the sinews of Adam HaRishon, as opposed to the Flesh [which is more "external"].  This is in order to draw life to the entire root.