"The genius of the moral teachings of Jesus and his first students was his insistence that you cannot keep the law by trying not to break the law. That will only make a Pharisee of you and sink you into layers of hypocrisy. Instead, you have to be transformed in the functions of the soul so that the deeds of the law are a natural outflow of who you have become. This is spiritual formation in the Christian way, and it must always be kept in mind when we consider Jesus’s teaching about various behaviors – in the Sermon on the Mount and elsewhere.
For example, his famous teaching about turning the other cheek. If all you intend is to do that, you will find you can do it with a heart still full of bitterness and vengefulness. If, on the other hand, you become a person who has the interior character of Christ, remaining appropriately vulnerable will be done as a matter of course, and you will not think of it as a big deal."
- Dallas Willard, The Great Omission," p. 152