Agni Purana (Jyotisha Selections) · by Vyasa
Chapter 2 · War Astrology: Yogas, Nakshatras
युद्धजयार्णवः (योगाः नक्षत्राणि)
पञ्च वर्गाः स्वरा जाताः कुजज्ञगुरुभार्गवाः ।शनिः क्रमादकाराद्याः ककाराद्यास्त्वधः स्थिताः ॥
In the full Agni Purana this is chapter 124, verse 14.
The five letter groups were born from the vowels: Mars, Mercury, Jupiter, Venus and Saturn, in order, starting from a. The letters beginning with ka stand below.
Simple meaning: The five letter groups come from the vowels and match Mars, Mercury, Jupiter, Venus and Saturn in order.
एतन्मूलमतः सर्वं ज्ञायते सचराचरम् ।
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.