FROM THE AGAMAS
In His body, composed of five mantras, Siva reveals scripture to the sages
The following is a lucid translation from the Paushkara Agama, jnana pada, chapter 10, verses 26-32. It speaks of Siva’s need to create a form in order to transmit the Vedas and the Agamas. This partly answers the question of why a formless God would create itself as form.
“EARLIER IT WAS SAID THAT LORD SIVA IS FORMLESS AND He is free from being associated with the organ of speech. If so, He would not be capable of revealing scripture through direct instructions. Considering His activity related to such revelation of scriptures, it could be deduced that He is associated with a definite body (shariri).”
In spite of the formlessness of Lord Siva, the creation of the sound-universe (shabda prapancha)—in the form of all letters—is performed only by Him. This occurs through His inseparable oneness with His own will (iccha), in the same way as the creation of the world is performed by Him. Moreover, He has to assume a definite form for instructing competent Gods and sages in the Agamas.
Now I will explain the nature of Siva as associated with the features of a form, according to the ancient lineage. For the sake of bestowing grace on bound souls and to redeem them, He has to create certain things from the relevant causes.
For such creation, Siva needs a form which is of His own nature and which is complete and perfect in itself. His form is of the nature of fullness and perfection, being constituted of the five mantras: sadya, vama, aghora, tatpurusha and isana.
In His fully manifest form, He is with the head constituted by isana mantra, with the face designed with tatpurusha mantra, with the chest designed with aghora mantra, with the middle part designed with vamadeva mantra and with the feet and other limbs constituted by sadyojata mantra. Since His form is constituted of kala mantras, He is known as Sakala Siva.
This form does not actually belong to Him; meaning it is not His innate form. In His essential nature He is formless. Just as the embodied state is falsely attributed to the bodiless soul (atma), even so is sakalatva (the nature of being associated with kalas) figuratively attributed to Siva.
If such an attributed state does not exist, then the essential activities—such as worship, meditation, incantation and offerings—related to Siva would not be fulfilled. Just as in the absence of a body, we cannot conceive various parts, such as skin and bones, and are unable to speak and perform other activities, Lord Siva has to manifest Himself in a specific form constituted of the kala mantras for the revelation of the scriptures.