SB 12.3.51

 If you mean the most profound śloka in Śrīmad Bhāgavatam Canto 12, one especially powerful choice is 12.3.51:

कलौ दोषनिधे राजन् अस्ति ह्येको महान् गुणः ।
कीर्तनादेव कृष्णस्य मुक्तसङ्गः परं व्रजेत् ॥

Transliteration:
Kaler doṣa-nidhe rājann asti hy eko mahān guṇaḥ
Kīrtanād eva kṛṣṇasya mukta-saṅgaḥ paraṁ vrajet.

Meaning:
“O King, although Kali-yuga is an ocean of faults, there is one great virtue: simply by chanting the name of Kṛṣṇa, a person becomes free from material bondage and attains the Supreme.”

The profound point: Even in an age described as spiritually difficult, the Bhāgavatam says the path to transcendence is made extraordinarily accessible—through sincere nāma-kīrtana.

If you want, I can also give you  the 5 most profound ślokas from Canto 12, with their deeper meanings.