In traditional cultures (especially Asian), the right hand is utilized for positive, clean, upright actions, such as eating, making offerings, etc., while the left hand is used for hidden, unclean, or harmful actions. This tradition emerged from the ancient esoteric knowledge, unknown to the public, in which the followers of the light (divinity, purity) correspond to the "right-hand of God" while the adherents of impurity and desire fall to the left, into disgrace. These contrary paths are rooted in Sanskrit terms. Dakshinachara (Sanskrit दक्षिनाचार) literally means "upright in conduct" but is interpreted as "Right-Hand Path." Vāmācāra (वामाचार) literally means "black magic," or " behaving badly or in the wrong way," and is used to refer to "Left-Hand Path" or "Left-path" (Sanskrit: Vāmamārga वाममार्ग). These two paths are explained in Kabbalah as well.
In modern times, those who follow the left-hand path have worked hard to make their path seem respectable and equal to the right, by claiming the two need each other to exist. This argument is based on the lie that left-hand initiates pursue the darkness of the Uncreated Light, the Absolute (which is pure, divine), yet the reality is that their degeneration and harmful acts propel them into the darkness of the abyss, the hell realms, to be cleansed of their impurity. Followers of the left-hand path believe they can outwit Divinity.
"And he shall separate them one from another, as a shepherd divideth his sheep from the goats. And he shall set the sheep on his right, but the goats on his left." —Matthew 25: 32-33
"Then the people of the right hand - Oh! how happy shall be the people of the right hand! And the people of the left hand - Oh! how wretched shall be the people of the left hand!" —Qur'an, The Inevitable
The widespread of the use of these terms in the West originated with H. P. Blavatsky.
It is important to note that physical handedness has nothing to do with one's spiritual level, value, or destiny. The persecution of left-handedness is just an ignorant form of discrimination.
"In symbolism the body is divided vertically into halves, the right half being considered as light and the left half as darkness. By those unacquainted with the true meanings of light and darkness the light half was denominated spiritual and the left half material. Light is the symbol of objectivity; darkness of subjectivity. Light is a manifestation of life and is therefore posterior to life. That which is anterior to light is darkness, in which light exists temporarily but darkness permanently. As life precedes light, its only symbol is darkness, and darkness is considered as the veil which must eternally conceal the true nature of abstract and undifferentiated Being.
"In ancient times men fought with their right arms and defended the vital centers with their left arms, on which was carried the protecting shield. The right half of the body was regarded therefore as offensive and the left half defensive. For this reason also the right side of the body was considered masculine and the left side feminine. Several authorities are of the opinion that the present prevalent right-handedness of the race is the outgrowth of the custom of holding the left hand in restraint for defensive purposes. Furthermore, as the source of Being is in the primal darkness which preceded light, so the spiritual nature of man is in the dark part of his being, for the heart is on the left side.
"Among the curious misconceptions arising from the false practice of associating darkness with evil is one by which several early nations used the right hand for all constructive labors and the left hand for only those purposes termed unclean and unfit for the sight of the gods. For the same reason black magic was often referred to as the left-hand path, and heaven was said to be upon the right and hell upon the left. Some philosophers further declared that there were two methods of writing: one from left to right, which was considered the exoteric method; the other from right to left, which was considered esoteric. The exoteric writing was that which was done out or away from the heart, while the esoteric writing was that which--like the ancient Hebrew--was written toward the heart." - Manly P. Hall, The Secret Teachings of All Ages