20 The soul is immortal, and all souls are alike both of men and women; for only the members of the body are distinguished. There is not a class of souls sinning by nature, and a class of souls practising righteousness by nature: but both act from choice, the substance of their souls being of one kind only, and alike in all. I know, however, that I am talking much, and that the time is already long: but what is more precious than salvation? Are you not willing to take trouble in getting provisions for the way against the heretics? And will you not learn the bye-paths of the road, lest from ignorance thou fall down a precipice? If your teachers think it no small gain for you to learn these things, should not thou the learner gladly receive the multitude of things told you?
Source: Catechetical Lectures (New Advent)