It would very much prevent our being misled by this self-partiality, to reduce, that practical rule of our Saviour, "Whatsoever ye would that men should do to you, even so do unto them," to our judgment and way of thinking. This rule, you see, consists of two parts. One is, to substitute another for yourself, when you take a survey of any part of your behaviour, or consider what is proper and fit and reasonable for you to do upon any occasion: the other part is, that you substitute yourself in the room of another; consider yourself as the person affected by such a behaviour, or towards whom such an action is done; and then you would not only see, but likewise feel, the reasonableness, or unreasonableness of such an action or behaviour. But, alas! the rule itself may be dishonestly applied: there are persons who have not impartiality enough with respect to themselves, nor regard enough for others, to be able to make a just application of it. This just application, if men would honestly make it, is, in effect, all that I have been recommending: it is the whole thing, the direct contrary to that inward dishonesty as respecting our intercourse with our fellow-creatures. And even the bearing this rule in their thoughts may be of some service: the attempt thus to apply it, is an attempt towards being fair and impartial, and may chance unawares to show them to themselves, to show them the truth of the case they are considering.
From Fifteen Sermons, Sermon X.