You know that in a community of many it is impossible for all to be of the same strength, whether in body or in character, and so the authority of the Rule advises us to bear each weakness with patience, and charity requires us to stoop down somewhat to each. Some other person sees this, and perhaps he begins to envy one whose pain he ought to share. Hence it happens that often in his heart he calls that person happy on account of the thing for which he should count him wretched, bearing his own need with difficulty.
Let this be the fruit of our sermon: that you be always mindful of higher things, because the fullness of humility consists of that. Perhaps the grace bestowed on you on a certain count seems greater than that given some other brother, but if you are a zealous rival, you will be able to judge yourself inferior on many counts. What if you are able to work or fast more than he, but he surpasses you in patience, outstrips you in humility, and towers over you in charity? Why do you meditate in foolish thought all day about what you seem to have? Be more concerned to know what you are lacking!
For the rest, be always mindful of what another possesses and you do not, because this thought preserves you in a humble state and distances you from as falling off into luke-warmness; but even more, it also enkindles in you a desire for improvement. We know that God opposes the proud but gives grace to the humble.
Bernard of Clairvaux, The Third Sermon for Sixth Sunday after Pentecost, CF 53, pp 128-129, 130