20 Once we have attained the truth in its fullness, integrity, and purity, unity should pervade our minds, hearts, and actions. For there is only one cause of discord, disagreement, and dissension: ignorance of the truth, or what is worse, rejection of the truth once it has been sought and found. It may be that the truth is rejected because of the practical advantages which are expected to result from false views; it may be that it is rejected as a result of that perverted blindness which seeks easy and indulgent excuses for vice and immoral behavior.
Source: Ad Petri Cathedram (Vatican.va)