Verse 4.4

यदुच्छ्वासनिःश्वासावेतावाहुती समं नयतीति स समानः । मनो ह वाव यजमान इष्टफलमेवोदानः स एनं यजमानमहरहर्ब्रह्म गमयति ॥ ४ ॥

yaducchvāsaniḥśvāsāvetāvāhutī samaṃ nayatīti sa samānaḥ | mano ha vāva yajamāna iṣṭaphalamevodānaḥ sa enaṃ yajamānamaharaharbrahma gamayati || 4 ||

4. (The priest) is he, samana, since he distributes equally the oblations which are inspiration and expiration. The mind is the sacrificer; the udana is the fruit of sacrifice; he leads the sacrificer every day to Brahman.

Shankara’s Commentary:

Com.—Here also, there is the priest officiating at the agnihotra. Because, he distributes inspiration and expiration (which are, as it were, the agnihotra oblations which are always double) for the support of the body; he is the officiating priest, as the carrier of the oblations, though already said to occupy the position of the fire (also). Who is this? He is samana; therefore, even the sleep of the knower is the giving of oblation in agnihotra. The drift, therefore, is that the knower should not be regarded as one performing no karma; for, it is said in the Vajasaneyakopanishad ‘even of him sleeping, all the Bhutas always perform sacrifices.’ Here, having thrown the external senses and objects as oblations into the wakeful Prana-fires and wishing to reach the Brahman, as one who would wish to reach heaven, the fruit of the performance of agnihotra, the mind, as sacrificer, wakes. Being known like the sacrifices as the most important of the effects and instruments, and having set out towards Brahman, as sacrificer to heaven, the mind is made the sacrificer. The fruit of the sacrifice is udana; because, the realization of the fruits of sacrifice is due to udana. How? The udana causing the mind, the sacrificer, to cease his own activity, conducts him every day during sleep to the undecaying Brahman, as to heaven. Therefore, udana occupies the place of the fruits of sacrifices.