The Law of Polarity says that everything can be separated into two wholly opposite parts, and each of those still contains the potentiality of the other.
Quantum physicists refer to a “wave nature of particles” and a “particle nature of waves” - each holds the potentiality for the other and each dualistically and simultaneously exist.
Every action has an equal and opposite reaction.
In the Kybalion, it is stated that “all truths are but half truths,” because each action contains a pair of reconcilable opposites.
All opposites seek to meet or know the other. The entire consciousness is playing a game of hide-and-seek with itself through polarity.
Without duality/polarity, there is no life, no contrast, no relativity, no time, no space, no definition.
We call Tantra a Non-Dual Yoga because it seeks to transcend the duality of the mind that sees things as self and other, good and bad, moral and immoral.
Tantra innerstands and outer stands that the inside is the outside as the breath is inhaled and exhaled, and the higher is the lower, as the rain descends and returns to clouds.
If a lion eats a zebra, she is killing and devouring an animal, yet predators like her strengthen the overall species by eliminating the sick and old that are hunted and no longer bred into the animal species. If you give a homeless man a dollar you may feel good, yet you may be reinforcing his sense of helplessness and keeping him disempowered. Most morality is, in actuality, split in this way.
In awareness, one rests in neutrality. Neutrality is the meeting and merging of duality.
The Gnostics have two paths to transcend duality. One is via purgativa (through purity), the other is via unitiva (through unity). One is to go towards the void, to empty oneself completely. The other is to go towards merging fully into love. Tantra is this merging into love.