The most important concept found in the tantras is the necessity of unifying (ceasing to separate) apparent opposites in order to attain enlightenment. These opposites are usually represented as male energy (Shiva) and female energy (Shakti) or as the individual (purusha) and nature (prakriti). Thus the equality, or complementarity, of male and female is a foremost aspect of tantric practice, as the union of both is required in order to achieve the highest understanding.
According to the tantras, male and female (or the individual and nature) are not really separate, but are only seen that way from the viewpoint of worldly phenomena. When one has achieved a state of perfect enlightenment the two will be seen as completely integrated. In fact the equilibrium of the two is considered to be the very nature of truth.
[Sharma, L.N. Kashmir Saivism. Varanasi: Bharatiya Vrdya Prakasham, 1972.]