Agni Purana (Jyotisha Selections) · by Vyasa
Chapter 2 · War Astrology: Yogas, Nakshatras
युद्धजयार्णवः (योगाः नक्षत्राणि)
एतन्मूलमतः सर्वं ज्ञायते सचराचरम् ।विद्यापीठं प्रवक्ष्यामि प्रणवः शिव ईरितः ॥ १५ ॥
In the full Agni Purana this is chapter 124, verse 15.
From this root all is known, with the moving and the unmoving. I will tell the seat of knowledge. Pranava (Om) is called Shiva.
Simple meaning: From this root all is known. Next the seat of knowledge is told, and Om is called Shiva.
उमा सोमः स्वयं शक्तिर्वामा ज्येष्ठा च रौद्र्यपि ।
Several goddesses and Brahma, Vishnu and Rudra are named, with the three qualities starting with creation.
रत्ननाडीत्रयं चैव स्थूलः सूक्ष्मः परोऽपरः ।
Think of the white one releasing the highest nectar through the three jewel paths.
प्लाव्यमानं यथाऽऽत्मानं चिन्तयेत्तं दिवानिशम् ।
Thinking of oneself as flooded by it, one becomes ageless and reaches Shiva-hood.