Bhashya
द्यौरेव उत् उच्चैःस्थानात्, अन्तरिक्षं गी गिरणाल्लोका-नाम्, पृथिवी थ प्राणस्थानात्, आदित्य एव उत् ऊर्ध्व-त्वात्, वायु गी अग्न्यादीनां गिरणात्, अग्नि थ याज्ञी-यकर्मार्वावस्थानात्, सामवेद एव उत् स्वर्गसंस्तुतत्वात्, य-जुर्वेदो गी यजुषा प्रत्तस्य हविषो देवतानां गिरणात्, ऋ-ग्वेद थम् ऋच्यध्यूढत्वात्साम्न ।उद्गीथाक्षरोपासनफलम-धुनोच्यते—दुग्धे दोग्धि अस्मै साधकाय, का सा ? वाक्,कम् ? दोहम्, कोऽसौ दोह इति, आह— यो वाचो दोह,ऋग्वेदादिशब्दसाध्यं फलमित्यभिप्रायः, तत् वाचो दोहं तस्वयमेव वाक् दोग्धि आत्मानमेव दोग्धि ।किंच अन्नवान्प्रभूतान्नः अन्नादश्च दीप्ताग्निर्भवति, य एतानि यथोक्तानिएव यथोक्तगुणानि उद्गीथाक्षराणि विद्वान्सन् उपास्ते उद्गीथइति ॥
In plain words
Heaven is 'ut' because of its high place; the atmosphere is 'gī' because it absorbs the worlds; the earth is 'tha' because prana rests there. The sun is 'ut' because it shines above; the wind is 'gī' because it absorbs fire and the other elements; fire is 'tha' because it stays in the lower place of sacrifice. The Samaveda is 'ut' because it is praised as heaven; the Yajurveda is 'gī' because the deities consume the oblation offered through it; the Rigveda is 'tham' because the Saman rests upon the Ṛc. Now is declared the fruit of meditating upon these syllables of the Udgitha: it yields its yield to the seeker. What is that seeker? Speech. What is the yield? The yield itself. Asking what that yield is, the text explains: whatever yield speech produces—the fruit attained through the Rigveda and other Vedic words—that very yield speech milks forth for itself. Moreover, whoever meditates upon these syllables of the Udgitha with this exact understanding becomes rich in food, possesses abundant food, consumes food, and glows with bright inner fire.
Close to the Sanskrit
Heaven indeed as 'ut' due to higher placement, the atmosphere as 'gī' from the swallowing of worlds, the earth as 'tha' from the seat of prana; the sun indeed as 'ut' from being upward, wind as 'gī' from swallowing Agni and others, fire as 'tha' from abiding in lower sacrificial works; Samaveda indeed as 'ut' from being praised as heaven, Yajurveda as 'gī' from the swallowing of the oblation offered by Yajus, Rigveda as 'tham' from the Saman being mounted upon the Ṛc. The fruit of meditating on the syllables of Udgitha is now stated: it milks, it milks for this seeker—which one? Speech. What? The milking. What is that milking? It says: whatever is the milking of speech, meaning the fruit attainable by words like Rigveda etc., that very milking of speech speech itself milks, it milks the self alone. Furthermore, he who knowing these very syllables of Udgitha with the stated qualities meditates, becomes possessor of food, with abundant food, an eater of food, and with blazing fire.