The Three Skills
1. Pubbenivasanussati-ñana: the ability to remember past lives.
2. Cutupapata-ñana: the ability to know where living beings are reborn after death.
3. Asavakkhaya-ñana: the ability to do away entirely with the effluents of defilement.
1. The ability to remember past lives: First you have to be proficient in all four frames of reference (satipatthana). Once your powers of reference are strong, you will know the truth of the body in the present. That is, you keep focusing on the body as it appears in the present until there appears the subtle image of the body that is constantly arising and falling away. You will then be able to know not only the present, but also the past and future of the body. With regard to the past, you will know back to the day it was conceived in your mother's womb. What it was like after the first day, the seventh day, one month, three months, seven months, nine... what it looked like, how it lived, what sort of food it consumed; and then as it grew one year, two, three, four, five all the way to the present: You'll be able to know the truth of the body. As for the future, you'll know how the body will change if you live to the age of thirty, forty, eighty, all the way to the day you die. If your knowledge on this level and your powers of reference are truly strong, you will be able to remember back one lifetime, ten lifetimes, one hundred, one thousand... depending on the power of your mind. As for the mental phenomena you experienced in past lives, you will be able to know them as well, just as you can know the body.
2. The ability to know where living beings are reborn after death: First you have to be proficient in knowing the movements of your own mind in the present. Sometimes it takes on the characteristics of a mind in the realms of deprivation, sometimes the characteristics of a human mind, a heavenly mind or a Brahma mind. Once you know your own crude and subtle mental states in the present — and if your knowledge is truly strong — you will be able to know, via the inner eye, exactly how well or badly different living beings fare when they die.
3. The knowledge that does away with the effluents of defilement: This means clear knowledge of the four Noble Truths — the ability to diagnose stress (dukkha) as arising from craving (tanha); the ability to pinpoint what will put an end to craving, i.e., identifying the path (magga), and then following the path until the disbanding of stress (nirodha) occurs. You will have clear vision of all four truths, doing away with defilement, craving, views, and conceits through the power of your discernment. The knowledge that does away with mental effluents forms the essence of liberating insight (vipassana-ñana).