The royal sages knew this yoga, handed down in this way from one to the next. But over a long span of time, O Parantapa, that yoga was lost in this world.
Explanation
Krishna continues telling Arjuna how this yoga passed from Vivasvan to Manu to Ikshvaku, and then through the royal sages (rājarṣi), kings who were also seers. He says that over a long time the unbroken line of teaching lapsed. Here yoga means the discipline of selfless action joined with knowledge, which the Gita goes on to teach; commentators differ on whether it stresses karma-yoga or the wider path to liberation. "Parantapa", "scorcher of foes", is an epithet of Arjuna.