If there are mitzvahs that a person is able to fulfill and the opportunity arises to do so and he does not fulfill them, or if he has the ability to bring them about and yet doesn’t, then he will have to reincarnate until he completes them.

Take an opportunity to do something good when it presents itself.

It is therefore very important to take an opportunity to do something good when it presents itself. It could save having to go through a whole other lifetime!

However, regarding mitzvahs he cannot perform without G‑d creating the necessary circumstances, such as redeeming the first born son, yibum or chalitza, divorce, and similar, it will depend.

For example, if G‑d did create the necessary circumstances to fulfill any of them and he did not [fulfill that mitzvah], then he will have to reincarnate to fulfill which ever one he could have fulfilled but did not.

However, if the occasion did not arise to fulfill them, then he will not have to reincarnate to perform them, but rather, he will only come back b’sod ibur into a person who is undergoing that particular mitzvah and fulfill his obligation that way. Once the mitzvah has been completed, then he will return to his place.

Then there is a third level, which is the mitzvahs which cannot be performed today, such as sacrifices. Yet, we have stated that every person must fulfill all 613 mitzvahs and reincarnate until he does so! Thus, at this time he would not have to reincarnate for their sake since they cannot be performed. However, after Mashiach arrives and the Temple is re-built, may it be so speedily in our days, he will reincarnate in order to perform those particular mitzvahs .

"I will have to record this in my ledger for when the Temple returns"

Rebbi Yishmael, son of Elisha the High Priest, hinted to this when, after tilting the lamp on Shabbat night, he said, "I will have to record this in my ledger for when the Temple returns, so that I will then bring a substantial Sin-Offering" (Shabbat 12b).

He accidentally did a type of lighting fire, which is forbidden on Shabbat (Ex. 35:3).

Why did he record something in order to do something that could not be done? It must be that he knew that even if the Temple would not end up being rebuilt in his days (as it wasn't) that he would someday be able to bring the sacrifice, in a reincarnation.

From the mitzvahs that are not obligatory, such as reciting Shema Yisrael or tefillin

These mitzvahs need to be done every day – how can he speak of them as being optional? "Not obligatory" here does not mean that you don't have to do them. Rather it means that not doing them does not incur serious punishment. This is because the lack of fulfilling positive commandments is not as punishable as the transgression of negative commandments.

…there are mitzvahs that one need not pursue, such as sending away the mother bird, or putting up a parapet [on a roof], and which he may also have been prevented from completing. However, since he was not told to pursue and fulfill them, though the person will have to reincarnate he will definitely not sin in the upcoming gilgul.

This means to say that he will be protected from heaven in that lifetime, since he only came back to fix something that was never an absolute obligation.

However, if the mitzvah did present itself and he did not want to perform it, then he must reincarnate and in this case, there will be no guarantee that he will not sin.

Since the gravity of what he did was greater, the consequences are greater. He must come back without a guarantee of being protected.

However, one who actually transgresses and is thereby forced to reincarnate will most definitely sin again.

This needs to be understood in stages: The soul is intrinsically a pure simple light. No matter what bad deeds a person falls into, it does not affect his essence. However, it does taint the external aspects of the soul. This can be compared to a brilliant diamond. Even if it falls into the mud, it still really retains its beauty. The dirt only occupies the surface and prevents the light from shining out. As soon as the dirt is cleaned off, it resumes all of its glory.

The world was created for free will. A person must therefore bear the consequences of his actions. If he soiled his soul, he comes back in that state. It is his job - and actual claim to fame - to cleanse himself. However, he must know that he's not starting with a clean slate, rather from being in the negative. Therefore he will have certainly tendencies to do bad. This is what the Ari means by saying he will sin again. The person must be strong to withstand the test.

A person must fulfill all the 613 Mitzvahs in deed, verbally, and in thought.

Not only this, but a person must fulfill all the 613 Mitzvahs in deed, verbally, and in thought, ..

These are the three garments of the soul (Tanya). They come from the three triads of the sefirot. Thought comes from chaba"d – chachma/bina/da'at, speech comes from chaga"t – chesed/gevura/tiferet, deed comes from neh"i – netzoch/hod/yesod.

In order for the connection to be complete, it must be from all of our attributes to all of G‑d's. "I am to my beloved, and my beloved is to me" (Songs of Songs 6:2). Just as the simple Infinite light expresses to us, above to below, through these garments of the sefirot, so does the simple light of the soul express and connect to G‑d through its counterpart clothes: thought, word, and deed, below to above.

…as the Sages have said on the verse, "This is the law for the Burnt-Offering and the Meal-Offering" (Lev. 7:37): Anyone who learns the section of the Burnt-Offering is like one who offered it (Menachot 110a). They were indicating that a person is obligated to fulfill all 613 Mitzvahs verbally, and in thought as well.

The simple explanation of this teaching is that even when there is no Temple, there is some way that we can, as if, bring the sacrifices. When you learn about something, its root energy above is activated and channeled to the world. (How much it is activated depends upon how deeply you engage in delving into it.)

The same applies to meditating. There is even some category that doing something through learning and meditation is actually higher than doing in deed. The faculty of thought is higher than that of action. Some tzadikim are so able to be focused in the world of thought that they are able to make the rectification and fulfill their obligation through thought alone. Thus we found that Rabbi Shimon bar Yochai was exempt from doing mitzvahs because of his exalted level of meditation and learning.

The Ari comes to point out a lesson hidden and hinted in this rabbinical teaching, that there is an obligation to do all the mitzvahs also in thought and speech. If thought and speech were only optional, they would not be powerful enough to fuel a makeshift, 'winged' fulfillment of the mitzvahs when deed is not possible.

A person must learn Torah on four levels.

If a person fails to fulfill all 613 Mitzvahs on all three levels of deed, speech, and thought, then he will have to reincarnate until he does. As well, a person must learn Torah on four levels, alluded to by the word "PaRDeS," which stands for "Peshat," "Remez," "Drash," and "Sod." He will have to reincarnate until he does.

As explained in Chapter 11, that there are four primary levels of interpreting the Torah: Pshat (simple understanding), remez (hint), drash (exegetical), and sod (secret).

Learning Torah is the foundational root of all of the other mitzvahs. The comparison of the need to fulfill everything in thought word and deed to the necessity of learning the entire Torah comes to show that learning corresponds to all of the commandments (Pe'ah). The depth and breadth of the mind and heart must be connected to G‑d. One does this through learning the whole Torah, to its full length and width.

[Translation and commentary by Perets Auerbach.]