The Supreme (Shiva) creates the Universe and its beings through the ‘Linga (Penis)’ and ‘Yoni (Vagina)’ maintains the Universe and its beings through his blessing hand withdraw through the serpent as soon as the maintainer stops giving protection to the beings created by Lord Brahmaa.
Shiva is HE, the creator, maintainer and the withdrawer of every living and non-living thing. HE is Deva-Adhi-deva’ meaning ‘The Supreme of the gods’ i.e. ‘Mahaa Devaa’. Learneds say ‘HE is Formless’. I do not agree. He also has his own form but has not revealed HIS true form to anyone. No doubt, He can assume any form. We cannot say whether the description of ‘Mahesvara’ has been made out of illusions and assumptions by the yogis or out of seeing His various manifestations or by real visualization of his true form with his grace. While Shiva can manifest his power anywhere, without interruption, his incarnations manifested out of his limbs can perform only their appointed mission.
Our ancients included Shiva in the lineage of Trimurti (Trinity); whereas, in my opinion, Shiva in his purest form does not form part of Trinity. He is beyond the lineage of Trinity. Shiva is the creator of the trinity -viz Brahmaa, Vishnu, and Rudra, although Rudra embodies Shiva directly like that of Mahaa-Vishnu. Thus the actual lineage of Trinity is – Brahmaa, Vishnu (not Mahaa-Vishnu) and Rudra.
According to the ‘Trinity Theory’ mentioned in the Narada Purana, Lord Mahaa-Vishnu divided himself into three forms according to guna (quality/prosperity). Brahmaa of Rajo-guna was created from the right side of Mahaa-Vishnu for the creative activities; Vishnu of Sathva-guna was created from his left side for the maintenance and protection of the Universe and its beings and Rudra of Tamo-guna was created from the chest of Mahaa-Vishnu for the destructive.
Thus it may be seen that Lord Shiva is not included in the lineage of Trinity so is Lord Mahaa-Vishnu. This contention clearly indicates that Lord Mahaa-Vishnu and Lord Shiva are one and the same Supreme God.
Shiva is the withdrawer, whereas Rudra is the destroyer and savior. Shiva will involve himself only in the withdrawal of the cosmos and its beings at the end of each Kalpa (Aeon). All other destructive activities have been assigned to Rudra, who is one of Shiva’s direct manifestations. That is why we human beings have been directed by Lord Shiva himself that Rudra must be satisfied through worship, praise and hymns if we have to escape the wrath of Rudra so as to have a peaceful existence in this world. This direction of Lord Shiva establishes the fact that Lord Shiva and Lord Rudra are two separate personalities.