Aquinas believed there is an ‘ideal’ universal uniform human nature which all humans can potentially achieve. Aquinas stated that humans should ‘do good and avoid evil’. He believed that people didn’t deliberately choose to be evil. All people (religious or not) can know what is right or wrong using our ability to reason.
He quotes St Paul in Romans Chapter 2v24 ‘ the requirements of the law are written on their hearts, their consciences also bearing witness.’
He believed that it should be our ultimate goal, or final purpose, of every human to re-establish a ‘right’ relationship with God and by doing so gain eternal life with God in heaven. He believes this needs to be done as this ‘right’ relationship was broken by Adam and Eve. It was their act of ‘original’ sin, when they disobeyed God in the Garden of Eden, that broke this ‘right’ relationship.