After describing the adulteration of the acts of sacrifice, austerity, and charity with the modes of material nature, Krishna now gives us a practical way to purify these acts as well as our consciousness to go beyond the modes.

The mantra, oṁ tat sat (oṁ tat sad iti) is used (smṛtaḥ) to indicate (nirdeśo) Brahman [Supreme Spirit] (brahmaṇas) in three ways (tri-vidhaḥ). The brāhmaṇas (brāhmaṇās), the Vedas (vedāś), and (ca) the sacrifices (yajñāś) were created (vihitāḥ) with these sacred syllables (tena) in the beginning (purā). (BG 17.23)

Therefore (tasmād), the transcendentalists [aiming for Brahman realization] (brahma-vādinām) always (satataṁ) begin (pravartante) the performances of sacrifice, charity, and austerity (yajña-dāna-tapaḥ-kriyāḥ) in accordance with scriptural regulations (vidhānoktāḥ) with the chanting of (udāhṛtya) the syllable (ity), oṁ (oṁ). (BG 17.24)

Those transcendentalists seeking liberation (mokṣa-kāṅkṣibhiḥ), not aiming for (anabhisandhāya) some mundane result (phalaṁ), perform (kriyante) various (vividhāḥ) acts of sacrifice, austerity (yajña-tapaḥ-kriyāḥ), and charity (dāna-kriyāś ca) with the chanting of the sound (ity), tad (tad). (BG 17.25)

The sound (ity), sad (sad) is chanted (etat prayujyate) on the platform of Truth (sad-bhāve) and (ca) in saintly disposition (sādhu-bhāve), and (tathā) the sound, sad (sac-chabdaḥ) is chanted (yujyate) to preside over auspicious actions (praśaste karmaṇi). And (ca), being established (sthitiḥ) in sacrifice, austerity, and charity (yajñe tapasi dāne ca) is said (ucyate) to be sad (sad iti) and also the actions (karma caiva) for that purpose (tad-arthīyaṁ) is certainly (eva) called (abhidhīyate) sad (sad ity). (BG 17.26-27)

Krishna concludes this section as follows. Without faith (aśraddhayā), whatever (yat) action (kṛtaṁ) is done as a sacrifice (hutaṁ), charity (dattaṁ), and (ca) austerity (tapas taptaṁ) is said to be (ity ucyate) not sad (sad), and (ca) that is (tat) sad neither in this life (no iha) nor the next (na pretya). (BG 17.28)

In summary, faith is the most essential ingredient in making our actions transcendental.