B.G 17.27 and 28

यज्ञे तपसि दाने च स्थितिः सदिति चोच्यते। कर्म चैव तदर्थीयं सदित्येवाभिधीयते ॥२७॥

yajñe tapasi dāne ca sthitiḥ saditi cocyate। karma caiva tadarthīyaṃ sadityevābhidhīyate ॥27॥

[यज्ञे (yajñe) - in sacrifice; तपसि (tapasi) - in austerity; दाने (dāne) - in charity; च (ca) - and; स्थितिः (sthitiḥ) - steadiness; सत् (sat) - real; इति (iti) - thus; च (ca) - and; उच्यते (ucyate) - is said; कर्म (karma) - action; च (ca) - and; एव (eva) - certainly; तदर्थीयं (tadarthīyaṃ) - for that purpose; सत् (sat) - real; इति (iti) - thus; एव (eva) - certainly; अभिधीयते (abhidhīyate) - is called;]

Steadiness in sacrifice, austerity, and charity is referred to as 'sat', i.e. real, and so also is the action taken for that purpose.

अश्रद्धया हुतं दत्तं तपस्तप्तं कृतं च यत्। असदित्युच्यते पार्थ न च तत् प्रेत्य नो इह ॥२८॥

aśraddhayā hutaṃ dattaṃ tapastaptaṃ kṛtaṃ ca yat। asadityucyate pārtha na ca tat pretya no iha ॥28॥

[अश्रद्धया (aśraddhayā) - without faith; हुतं (hutaṃ) - offered; दत्तं (dattaṃ) - given; तपः (tapaḥ) - austerity; तप्तं (taptaṃ) - performed; कृतं (kṛtaṃ) - done; च (ca) - and; यत् (yat) - which; असत् (asat) - unreal; इति (iti) - thus; उच्यते (ucyate) - is said; पार्थ (pārtha) - O son of Pritha; न (na) - not; च (ca) - and; तत् (tat) - that; प्रेत्य (pretya) - after death; नः (naḥ) - for us; इह (iha) - here;]

O son of Pritha, whatever is offered, given, or performed without faith is considered 'asat', i.e. unreal. It benefits us neither in this life nor in the afterlife.

॥ ओं तत्सदिति श्रीमद्भगवद्गीतासु उपनिषत्सु ब्रह्मविद्यायां योगशास्त्रे श्रीकृष्णार्जुनसंवादे श्रद्धात्रयविभागयोगो नाम सप्तदशोध्यायः ॥

॥ oṁ tatsaditi śrīmadbhagavadgītāsu upaniṣatsu brahmavidyāyāṁ yogaśāstre śrīkṛṣṇārjunasaṁvāde śraddhātrayavibhāgayogo nāma saptadaśādhyāyaḥ ॥

[ओं (oṁ) - Om; तत् (tat) - that; सत् (sat) - truth; इति (iti) - thus; श्रीमद्भगवद्गीतासु (śrīmadbhagavadgītāsu) - in the glorious Bhagavad Gita; उपनिषत्सु (upaniṣatsu) - in the Upanishads; ब्रह्मविद्यायां (brahmavidyāyāṁ) - in the knowledge of Brahman; योगशास्त्रे (yogaśāstre) - in the science of Yoga; श्रीकृष्णार्जुनसंवादे (śrīkṛṣṇārjunasaṁvāde) - in the dialogue between Sri Krishna and Arjuna; श्रद्धात्रयविभागयोगो (śraddhātrayavibhāgayogo) - the Yoga of the Division of the Threefold Faith; नाम (nāma) - named; सप्तदशोध्यायः (saptadaśādhyāyaḥ) - seventeenth chapter;]

'Om Tat Sat'. Thus, the seventeenth chapter of the Bhagavad Gita, named 'The Yoga of the Division of the Threefold Faith', is declared in the Upanishads, in the knowledge of Brahman, and in the science of Yoga, through the dialogue between Sri Krishna and Arjuna ends.