Bhakti is devotion. Kṛṣṇa says it is through devotion that one comes to know him as he truly is.
Going deeper
Near the end of the Gītā, in chapter 18, Kṛṣṇa describes how a person grows into devotion. 18.54 says that one who has realised the state of Brahman, who is tranquil, who neither grieves nor craves and who regards all beings alike, attains supreme devotion to him. 18.55 says what that devotion does: through it the person comes to know him fully, who he is and how he is, in truth, and having known him thus, enters into him. 18.56 adds that someone who takes refuge in him and keeps performing all works attains the eternal abode by his grace. So bhakti here is not only a mood. It is a way of knowing, and it goes together with work. The passage is in chapter 18, and what the Gītā says about devotion gathers more.