As much use as there is in a tank when water floods everywhere around, so much is there in all the Vedas for a discerning brahmin.
Explanation
Krishna continues from the previous verse, where he told Arjuna to rise above the three qualities (guṇas) that the Vedas deal with. Here he gives an image: when water covers everything, a small well or tank adds little. In the same way, a brahmin who truly knows (vijānataḥ) finds the Vedas' ritual teachings of limited use. Some traditions take this to mean that ritual is surpassed by self-knowledge; others take it to mean that the Vedas are fulfilled in that knowledge.