In plain words
The poet, to his heart: Born a cowherd, he grazed the herds of cows, playing the flute [to gather them]; with skill he tore apart the horse [Kēśi]; and this Lord coloured like a sapphire, taking, as befitted him, the lion form [Narasiṃha], tore open the chest of Hiraṇya with his claws: know his wrath, [O heart].