Based on Mamar Mikveh Yisroel – There is a lot more there, we are just bringing down the easy concepts.

Before the sin of Adom the world was in a semi physical state leaning strongly to the spiritual side. When Adom sined he caused the whole world to physicalise. However waters represent the essence of purity and therefore did not become contaminated by the sin. They therefore retain a very high spiritual state, when one immerses in them he purifies himself. This is the meaning of the Medrash (Medrash Konen) that the lower waters wanted to rise up and join the upper waters until G-D kicked them down. The meaning is that they should have remained totally spiritual since they were unaffected by the sin. However G-D had mercy on the world and placed it in semi physical mater so sinners trying to repent can purify themselves.

Water manifest from the Upper Loving Kindness (Chesed) whose source is the Wisdom (Chochma) which is called Father (Abba). At this level there are no Klipot and external forces. These upper waters then manifest and filter through thousands of realms until they reach their physical state. When G-D wants to remove the control from the wicked forces and rulers, he brings forth the energy of the Chesed coming from Chochma. From this energy all the negative forces flee in panic. So too when a person enters the waters of the Mikvah, which is a lower manifestation of this energy, all the evil forces flee in panic.

One has to be very careful that he has no separating barrier on him when he immerses in the Mikvah (such as a band aid or dirt).

One has to make sure that he is fully immersed in the water and that not even one hair is sticking out.

There are Four Hundred main Camps of Impurity which manifested in the Four Hundred Men of Esav. The Mikvah contains Forty Seah each of which contain ten smaller units. When one immerses in the Mikvah each Seah removes Ten Camps of Impurity.

It is known from the Kabbalists that a person who immerses in the Mikvah even if he is unable to meditate on any of the Divine Names, he still brings upon himself a mighty spirit of purity.

Mikvas are not social bath houses and are not meant for entertainment and should not be used as places of relaxation.

There are only two Mitzvos that a person can immerse his whole body in, Mikvah and Sucah. A person who does not go to the Mikvah every day should at least do so on Sucot.

When a person immerses, he should meditate that as he is immersing bellow, his soul is immersing above in the fiery river of Dinor. For whatever a person does bellow, he causes his soul to do the same above.

It is very important for a person to bring himself to have some thought of repentance before he enters the Mikvah.

Even a person who regularly refrains from doing Kavanot and Meditating on divine names, since he considers himself unworthy and these things above his level. However the Kavanas of the Mikvah, every single person is permitted to make use of them, for the holiness of the Mikvah protects them.

If a person sees the forces of evil in a dream or vision (If a person is steeped in Pgam Bris they will look like women) he should immediately go immerse in a Mikvah even though he did not experience an emission. This is a sign that the forces of evil are lurking about him, waiting in ambush to defile him, as soon as they get a chance. One should immediately go destroy them in the Mikvah. This is mentioned in the words the Magid spoke to the Bais Yosef.

When a person has a family member who is heaven forbid sick, he should go to the mikvah for it can help. He should also dress in white.

It is known to the Kabbalists that there are three ways to rectify the soul. The first is through Fasting and Segufim. The second is through Crying and Tears and the third is through immersion in Mikvas.

It is very very important to immerse in a Mikvah on Erev Yom Kipor.

It is brought down by the Ari and the Rokach that before a person starts doing Teshuvah and a set of Segufim he should first try to immerse in a Mikvah.

Many famous Kabbalists would not let a person enter their room unless he had first immersed in a Mikvah.

Every person is surrounded by hundreds of Nigay Beni Adom (Afflictions of man) and Ruach Zenunim (Spirits of impurity) as well as many other categories of Klipot and external forces. These were created by all his sins in Action, Speech and Thought. Especially those created by Pgam Habris, these are fully considered his children. They follow him around all the time, every second of his life and even after his death. They do not leave his soul until it has been very purged and they are killed off by the suffering. When a person immerses in a Mikvah for the sake of purifying himself, all these forces temporarily leave him. When they leave him, he must use this time to strengthen his soul. Even though they return afterward, each time he dips for the sake of heaven of purifying himself, many of them are killed and exterminated.

There is also another element of negative energy, this comes from the inside of a person, this is his evil inclination (Yetzer) and the damaged parts of the soul. (This is why people feel Tzimzumim even when they are underwater). These do not leave him, but if a person is smart he can utilize the time in the Mikvah to rectify and purify these as well. The purity of the Mikvah reaches these as well. This is especially true in cold water.

Imagine to yourself two people; one is mercilessly beating up his friend. He is beating his head and body until it is filled with large ugly wounds. This exactly what a person does to his soul when he sins. When a person sins he beats his soul with cruel merciless blows, if a person could only hear the painful cries of his soul as he is beating it, he would not be able to withstand it for even a second. Now imagine a person who is very wasted, tired and weak. As he enters in cold water he suddenly regains his alertness. So too happens to the soul when it enters the Mikvah, it regains its alertness. The Mikvah cures and heals the soul. The effectiveness of this cure depends on the amount of sacrifice you had to go to the Mikvah, as well as the meditations that you do in it.

A big Kabbalist revealed to his students that the main levels he reached, was only from going to the Mikvah.

Know, that when you go to the Mikvah you remove part of your bad essence and destroy some of the thousands of Klipot surrounding you. You are also working to advance the rectification of the world as a whole.

There are two ways of sweetening the Judgments (Dinim) one is through money by doing a Pidyon Nefesh (redeeming the soul through money given to charity). The second is through the Mikvah. Even when a person does not have the power to nullify the Judgments, when he goes to the Mikvah he draws upon him Chasadim (Kindness). These intermingle with the Judjments and cause them to be less powerful.

A person has to be very careful not to think Torah or do Kavanot until he is in the water. He should be very careful not to do this in the dressing room or shower.

A person is not allowed to look at his own Bris and certainly not at his friend. A person has to be very careful not to look at the other people in the Mikvah.

It is very bad to talk to other people in the Mikvah. There are some very confused people who sit and socialize in the Mikvah while undressed. A fool like that is for sure causing much damage to his soul. A person should not spend an extra second undressed. If some one begins talking to you and you mast answer him for the sake of peace, then give him the shortest answer you can and try to get out of the conversation. A person should try his hardest not listen to the conversations of these foolish people who socialize in the Mikvah.

One must have at least these Kavanot in the Mikvah. Dip once to remove the impurity of the Sitra Acher. Dip a second time to draw Holiness on yourself and prepare yourself for prayer and Mitzvot.

It is also very important to have some thought of Teshuvah before immersing.

[Note: For Some Kavonot of the Mikvah look in Rabbi Aryeh Kaplans Medditation and Kabbalah]