Blademasters enter the Void in order to cut down their enemies. "The Flame and the Void" refers to the visualization of a flame in a void; all concerns - emotions, thoughts, even the concerns of life and death - are fed into the flame. This allows the blademaster to perceive reality as it is, in the present moment. Pain and fear become merely passing phenomena. The separateness of blademaster and enemy disappear.
Entering the Void allows the male channeler to seize saidin by perceiving light coming from the Void. Lanfear disguised as Selene, named this as "the Oneness" to Rand, in the alternate dimension as they chased after Padan Fain and the Horn of Valere.
Different Ways to the VoidEdit
Rand al'Thor first learned the Flame and the Void from his father, Tam al'Thor. While in the Void, Rand excelled in archery, and he would later also use it while performing sword forms. Without the Void, Rand discovered he was unable to perform the sword forms effectively. Later, being in the Void's brought Rand his first touch of saidin.
Lan Mandragoran uses something very similar to the Void, known to him as ko'di, to settle his mind during battle. When he was teaching the Emond's Fielders to use their weapons, he was very surprised to find that Rand, a farmboy, knew the skill already. Lan specifically mentions that it is not exclusive to blademasters.
Some martial artists, such as those training in Japanese Zen archery, use this state to allow the arrow to fly to its target at the most opportune time. Another example involves the Hindu hero, Arjuna, central to the Bhagavad Gita. Arjuna was able to hit a target with his arrow because he was able to precisely see a tiny target during the chaotic flow of battle. Many books and scrolls have been written on this subject, such as Issai Chozanshi's The Tengu's Sermon on the Martial Arts or a modern example, Peter Ralston's Cheng Hsin: The Principles of Effortless Power.
It should be noted that there are several paths to mindfulness. "The Flame and the Void" can be classified as a one-point meditation. In other one-point meditations, "The Flame" would be substituted for the breath or the tip of the nose. The concentration on doing exactly nothing is another, called wuxin in Chinese (mushin in Japanese). For more information on the practice of mindfulness, a good place to start is the book, Mindfulness in Plain English.