B.G 4.28

dravyayajñāstapoyajñā yogayajñāstathāpare। svādhyāyajñānayajñāśca yatayaḥ saṁśitavratāḥ ॥28॥

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.

dravyaṁ juhvatīti dravyayajñāḥ। tapaḥ parameśvarārpaṇa buddhyā tatra juhvatīti tapoyajñā ityādi। idaṁ tapaḥ haviḥ। tat brahmāgnau juhomi tatpūjārtham iti homaḥ। tadarpaṇe eva ca homabudidhaḥ ॥28॥

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.