Because the word sat indicating Brahman is present in the most excellent or auspicious things, it should be used in all auspicious activities whether material or spiritual. That is explained in two verses. The word sat indicates Brahman (sad bhāve) and the seekers of Brahman (sādhu bhāve).

Sat is situated (sthitiḥ) in sacrifice and other works since it is the goal of those works. Any work suitable for serving Brahman (tad-arthīyam) such as cleaning the Lord’s temple, is called sat.

The Supreme Lord indicated by the word sat exists in all other excellent things. Therefore the word sat is used during the performance of all auspicious activities. This is expressed in two verses. The word sat is used to indicate brahman (brahma bhāve) and the knower of brahman (sādhu bhāve), such as in the phrase sad eva saumya (this is brhaman) and satāṁ prasaṅgāt (from association with the knowers of brahman). Therefore the word sat is suitable to use on auspicious actions such as upanayana and marriage. Bg 17.26, Bg 17.27, Bg 17.26-27 SaḤave SaaDau>aave c SaidTYaeTaTPa[YauJYaTae ) Pa[XaSTae k-MaRi<a TaQaa SaC^Bd" PaaQaR YauJYaTae )) 26 )) Yaje TaPaiSa daNae c iSQaiTa" SaidiTa caeCYaTae ) k-MaR cEv TadQasYa& SaidTYaevai>aDaqYaTae )) 27 )) sad-bhāve sādhu-bhāve ca sad ity etat prayujyate praśaste karmaṇi tathā sac-chabdaḥ pārtha yujyate yajṣe tapasi dāne ca sthitiḥ sad iti cocyate karma caiva tad-arthīyaṁ sad ity evābhidhīyate sat-bhāve—in the sense of the nature of the Supreme; sādhu-bhāve—in the sense of the nature of the devotee; ca—also; sat—the word sat; iti—thus; etat—this; prayujyate—is used; praśaste—in bona fide; karmaṇi—activities; tathā—also; sat-śabdaḥ—the sound sat; pārtha—O son of Pṛthā; yujyate—is used; yajṣe—in sacrifice; tapasi—in penance; dāne—in charity; ca—also; sthitiḥ—the situation; sat—the Supreme; iti—thus; ca—and; ucyate—is pronounced; karma—work; ca—also; eva—certainly; tat—for that; arthīyam—meant; sat—the Supreme; iti—thus; eva—certainly; abhidhīyate—is indicated.

What is permanent (sthitiḥ) in sacrifice, austerity and charity in terms of their objective being permanent, is indicated by sat. Acts for the purpose of the Lord (tad arthīyam) who is indicated by these three names, such as building or cleaning His temple, are called sat. One must remember these three names. This should be considered an injunction, thought the grammatical form does not indicate it. The statement made was oṁ tat sad iti nirdeśo brahmaṇas tri-vidhaḥ smṛtaḥ: these three names of the Lord were remembered. This is similar to statements such as vaṣaṭ-kartuḥ prathamaṁ bhakṣyaḥ: the food belongs to the priest uttering vaṣaṭ. These statements must be regarded as injunctions or orders, however, because of the rule of uniqueness (apūrva) laid down by Jaimini, in Jaimini Sūtra 3.5.21. [Note: If a statement is unique in its context, even if it is not in the form of an injunction, it should be understood as an injunction. The present statement “The wise remembered the three names of Viṣṇu.” can then imply the following injunction: “We must remember the three names of Viṣṇū.”] Another reason for understanding the statement as an injunction is that uttering the names during sacrifice, charity and other actions, is necessary to remove all obstacles to attaining the final result. The smṛti says: pramādāt kurvatāṁ karma pracyavetādhvareṣu yat smaraṇād eva tad viṣṇoḥ sampūrṇaṁ syād iti śrutiḥ Whatever mistakes are committed in sacrifice out of inattention will be rectified by remembrance of Viṣṇu. This is the statement of the śruti. Garuḍa Purāṇa 1.230.13