Gehinnom is often translated as “hell,” although both the original Hebrew and common translations have myriad, not necessarily consistent, connotations.
For our purposes, let’s not call it hell.
The “punishments” of Gehinnom are meant to bring us to a state of purity.
Throughout our lives in this world, our souls absorb life’s events and are affected by them.
Among these events are moments of enlightenment that the pure soul in itself would not have been able to reach had it not been connected to a body, because such experiences attach to the soul only through the kinds of tools the body can provide, such as worldly experiences.
But while embodiment allows the soul to develop in ways impossible without this experience, damage is also inflicted on the soul through embodiment, which can be likened to scars left by evil.
Gehinnom is the state in which all these injuries are rectified and removed from the soul.
The state of the deceased can be likened to one who removes clothing that has been worn for a long time and that is torn and stained.
Just as it is ridiculous to say that when a garment is laundered, it is undergoing punishment for its sins, so too, what a soul undergoes in Gehinnom should be seen not as punishment but as a cleansing.
–Rabbi Adin Steinsaltz