B.G 4.28

द्रव्ययज्ञास्तपोयज्ञा योगयज्ञास्तथापरे। स्वाध्यायज्ञानयज्ञाश्च यतयः संशितव्रताः ॥२८॥

Sacrifice in the form of self-study and knowledge, sacrifice in the form of Yōga, sacrifice in the form of practice, sacrifice in the form of offering wealth, and others are respectively the resolute observances.

Gīta Bhāshya 4.28

'dravyayajñāḥ' - offering of wealth. 'tapoyajñā' - practicing the attitude of offering to the supreme lord. The act of offering to the supreme lord alone is indeed the understanding of sacrifice, symbolized by oblation into fire.

द्रव्यं जुह्वतीति द्रव्ययज्ञाः। तपः परमेश्वरार्पण बुद्ध्या तत्र जुह्वतीति तपोयज्ञा इत्यादि। इदं तपः हविः। तत् ब्रह्माग्नौ जुहोमि तत्पूजार्थम् इति होमः। तदर्पणे एव च होमबुदि्धः ॥२८॥

They offer wealth, hence it is called 'dravyayajñāḥ', i.e. sacrifice of wealth. The word 'tapoyajñā', i.e. sacrifice of practice, means practicing the attitude of offering to the supreme lord. In this context, such a practice itself is oblation. The offering into the fire is - "With the purpose of worshiping Him, I offer into the fire of Brahman". The act of offering Him alone is indeed the understanding of sacrifice, symbolized by oblation into fire.