Mahavishnu, resorting to the three gunas created three forms. It is significant that even Vishnu, one among the Trimurti-s, is created along with the other two.
(There are very similar verses in the Vishnu puranam too.)
सृष्ट्यर्थं तु पुरा देवो दक्षिणाङ्गात्प्रजापतिम् ।। मध्ये रुद्राख्यमीशानं जगदन्तकरं मुने ।। ३-४ ।।
For the creation function He brought forth Prajapati (Brahmaa) from his right side. In the middle (of his own body) is Rudra, the dissolving force.
पालनायास्य जगतो वामाङ्गाद्विष्णुमव्ययम् ।।
For the sustaining function Vishnu issued forth from the left side of Mahavishnu's body.
This reminds us of a similar method in the Mahabharata where Shiva, from his own body sides created the Trimurtis:
The concept of Turiya Śiva is widely present in the scriptures. A sample of quotations are Mahabharata Anushasanika parva, Ch.45. Here Krishna says about Shiva that from Shiva have Brahma, Vishnu and Rudra have emerged.
That Primordial eternal Ishwara is called Shiva, Vishnu and Brahmaa by various persons. This shows that the Primordial Lord is known by all the three names.
The Shakti, power of that Supreme God is the one that engages in the creation of the world. It is existent and non-existent and is both Vidya and Avidya.
O Narada, when the distinctions between the knower, known and knowing (TripuTee) is gond (due to right knowledge), then the vision of Unity - sarva eka bhaavanaa, arises which is called vidya.
एवं माया महाविष्णोर्भिन्ना संसारदायिनी ।। अभेदबुद्ध्या दृष्टा चेत्संसारक्षयकारिणी ।। ३-९ ।।
Thus when Maya is seen as a distinct, standalone entity apart from Vishnu, then one is in the throes of samsara. On the other hand when Maya is known to be non-different from Maha Vishnu, then liberation results. The point is that Maya does not have an independent existence.
Just as ether/space appears divided owing to the adjuncts (upadhis) so too due to the avidya upadhi this entire world appears divided (sva gata bheda)
The One Shakti of Brahman is given many names such as Uma, Lakshmi, Bharati, Girija, Ambika, Durga, Bhadrakali, Chandi, Maheshwari, Kaumari, Vaishnavi, Vaaraahi, Aindri, Shaambhavi, Braahmi, VidyAvidyA, Maya, Prakriti, ParA - by Maharshis. (Incidentally, in the Sharada temple of Sringeri, during Navaratri, the deity is daily adorned in different forms and names given are many found in the above list.)
उमेति केचिदाहुस्तां शक्तिं लक्ष्मीं तथा परे ।। भारतीत्यपरे चैनां गिरिजेत्यम्बिकेति च ।। ३-१३ ।।
Even though He is Pure and Supreme, when associated with Ahankara, Ego, is termed a jiva by the ignorant ones. (That Brahman alone appears as the jiva due to ego-association is brought out here)