In plain words
The poet, to his heart: O my heart, think fully on the feet alone of the wondrous Lord of the great form, who need be no one's son [by karma] yet was born a son [to Vasudēva], and who cut off the [thousand] arms of Bāṇa when Bāṇa imprisoned the beloved son of his own son [Aniruddha, son of Pradyumna].