From Letter XIII:
 That very ambiguous maxim, which has been so generally instilled into the minds of our babies, “Be good, and every body will love you,” it is to be hoped, is nearly exploded. Could its influence be confined to childhood, it might do very well; because the pleasures and pursuits of children seldom clash with the interest of grown persons. But, should we be influenced by it when we have “put away childish things,” we shall find ourselves dreadfully deceived.
There is a certain speciousness, a plausibility, a semblance of goodness, which every one can see, and every one approve. But the real, substantial virtue, the purity of heart inculcated in the Gospel, is so contrary to the principles, the passions, and the pursuits of the world that it always has met, and every must expect to meet, its opposition. It is not because the heart condemns, and the judgment disapproves this. Probably there is no human being so depraved,  as to feel a real abhorrence of purity and goodness: it is only because their operations oppose his passions, militate against his plans, and check the career of his licentiousness, that the enmity of the vicious is awakened; and he who, braving sneers and censures, is enabled to persevere in goodness, may sometimes extort approbation from those who would have drawn him into the vortex of ruin. But as the effect is generally the same, virtue must look higher, or frequently be discouraged: it must have nobler motives, or often go unrewarded. What saith the Saviour to his disciples? “The world will love its own; and because ye are not of the world, but I have chosen you out of the world, therefore the world hateth you?”
There is a species of moral heroism requisite even in retired and domestic life, similar in its nature, to that which enabled the martyrs to meet the stake and the scaffold. This can be inspired only by motives too pure for the earthly-minded to comprehend; and it can be rewarded only by a recompence too noble for them to appretiate.
Mankind are so blind and so perverse that they sometimes cannot, and often will not, discriminate between semblances and realities, nor separate the precious from the vile. Happily for the Christian, he has higher aims than the  approbation of the world. The testimony of conscience, the plaudit of Heaven; these are the unerring witnesses whose favours he first seeks: if that of his fellow-men follow, he is not insensible to its value, as it is often an auxiliary ot his cause, as well as a stimulus to his zeal; but he dares not court it, he dares not depend upon it, knowing that it is frequently withheld from mistake, withdrawn from caprice.
It hath been often said, that were virtue to appear in a human shape, all mankind would love her! It seems strange that any who have read the New Testament should, for a moment, suppose this. Virtue has appeared, in all her loveliness. What was the consequence? It “was despised and rejected of men!” That greatest of characters, whose purity and excellence even his enemies acknowledge, was accused of “perverting the people,” and deemed unworthy to live! What was his treatment during life? What were the circumstances attendant on his death? Read the account, and you will learn the capability of mankind to appretiate excellence. Oh, that you might also be stimulated by that noble, that heavenly example, to bless them that curse you; to do good to them that hate you; to despise every thing which comes in competition with your  eternal interest; and, with an heart fixed on an inheritance incorruptible, to tread the narrow way which alone leadeth to it.
Truth is always desirable; nor is this view of it discouraging. Those who are incited to virtuous conduct by the hope of human approbation, suffer habitually from apprehension, and frequently from disappointment. A great number of instances might be selected from history, of persons, who, having been stimulated to noble actions by public applause, where unable to bear the mortification when popular favour turned against them, and have been driven, by desperation, to commit the most daring, the most awful of all crimes—suicide; while the truly humble and upright have enjoyed the most sublime consolations, when the world has most severely frowned. For though dignified and amiable characters may find their expressions sometimes misconstrued, and their actions misrepresented; yet the object they have in view is not endangered, nor will their conduct be relaxed, or their motives changed. “Great peace have all they that love thy law, and nothing shall offend them.”
Adieu, my beloved children; adieu. The happiness I wish you, is not a happiness that will vanish when the world frowns, or when  the breath of life departs; it is a happiness eternal, unchangeable as God himself. It must be sought (whether others approve or condemn, whether the palace or the dungeon be our abode) in endeavouring to be, in a measure, like him, “who did no sin, neither was guile found in his mouth.”