Regarding the performance of mitzvot, it is important to know that every limb from the 248 limbs of the soul of Adam includes its own set of 248 limbs.

...every individual spark contain something from the entire limb...

This will be an explanation as to why it is not sufficient for a person to perform only those mitzvot that are relevant to his root. For just as each limb incorporates something from the 248 Limbs and so every limb is obligated to fulfill all 613 mitzvot, so too does every individual spark contain something from the entire limb, and is therefore commanded to fulfill all 613 mitzvot. (Bnei Aharon)

Therefore, the entire posture of Adam was dependent upon it. Thus for example, someone who comes from the shoulder-limb includes 248 limbs from head to heel.

The entire macrocosm is included in the microcosm as it says, "Man is a small world." (Tanya IV, chap. 12) Therefore, "A person is obligated to say, 'The world is created for me' (Sanhedrin 4:5) and accordingly to seek to fix it." (Likutei Moharan 5) Since man actually includes in himself all aspects of all parts of existence, working to perfect himself is a method to fix the entire universe.

Someone whose soul is specifically from the heel of the shoulder does not have to rectify the entire shoulder and all its defects - just the level of the heel itself.1 However, if a soul-spark from the level of the heel caused a defect, then all the sparks of the heel do have to rectify this blemish, since all of the sparks of the heel are interdependent. When the entire heel is rectified, then not one spark will have to reincarnate to rectify any defects for the rest of the sparks of the shoulder.

Furthermore, if a spark from the heel transgresses in such a way as to necessitate reincarnation to rectify the damage, it will do so with another [spark] from the heel to help him rectify it. However, if the transgression was one that results in the destruction of the body (i.e., excision), then that spark alone will reincarnate into another body without a partner while the first body will be destroyed.

he will continue to do so until he completes all the 613 mitzvot.

If however he has to reincarnate only to make up for a mitzvah yet to be fulfilled, then he will not need to reincarnate with another spark - he alone will reincarnate into a second body. Thus, he will continue to do so until he completes all the 613 mitzvot. At the time of resurrection, all the bodies will return and take the portion that was completed while in them.

More than one body of the same person can resurrect! Each one will contain within it the sparks that were rectified during its specific gilgul.

[Translation and commentary by Perets Auerbach.]