"None of the furtive shabby manoeuvres of a younger son. I have sold my soul or you have sold it"
According to the British laws of primogeniture, all the father's property would be inherited by the oldest son. Younger sons could not depend upon inheritance, and had to earn their own living or marry well.
Rochester refers to the Faust legend – Faust sold his soul to the devil for knowledge. Christopher Marlow's Doctor Faustus and Goethe's Faust are reworkings of this legend.