"To err is human, to forgive is divine."
The statement is attributed to Alexander Pope but might be of ancient origin. The essence of it is that a human being is not perfect. There is no one, whether a saint or a sinner, who does not regret having done something in the past. The feelings of regret, remorse, and guilt are basically the same, the difference is only of degree. They are all related to one's conscience and they always pertain to the past.
This brings us to the question as to what is conscience. There is no generally accepted definition of conscience, but it supposes the existence of some faculty that produces feelings of approval or disapproval of one's own actions. In a sense it is a higher self judging the lower one. The feelings of approval create no problems but those of disapproval last long, sometimes, even life long. It is here that the degree comes into play and determines the intensity of the prick of the conscience.
Strangely enough these feelings do not necessarily relate only to things actually done but also to things not done that should or could have been done. This is especially so in the case of human relationships; the more intimate the relationship, the stronger is the feeling of remorse or guilt. It is an unfortunate fact of human nature that the importance of someone or something is felt more acutely in the absence, especially so when it has an element of finality.
Conscience is related to the faculty of discrimination, which in turn is an attribute of the consciousness. It is the discrimination between right and wrong according to one's inner beliefs that depend on the conditioning of the mind. This conditioning is a result of external factors like religion, upbringing, and environment. Therefore the concept of right and wrong varies in individuals covering an incredibly wide range. The feelings of remorse and guilt in different people may vary from nonexistent to overwhelming depending on the nature of their conscience.
The main problem related to these feelings is how to overcome them. Since they relate to past actions or lack there of, it is impossible to remove the root cause. The only thing that one can do is to learn from the error and avoid that kind of behavior in future. But in some cases even that may not be an option. Take for example, the remorse of a parent for having done (or not done) things to a child. The opportunity for doing or not doing those things is lost forever. So what is one to do?
This is where the significance of the above quotation comes in. We have to realize the fact that no one is perfect; everyone makes a mistake sometime or other. Forgiving is an act that takes away the effect of the mistake for both, the subject and object. It is divine, not in any religious sense but in the sense of purification of the Self. When it comes to forgiveness, the most difficult thing to do is to forgive oneself. The difficulty arises precisely because of the fundamental cause of all problems: the subject-object duality. In this case the offender and the offended are one, even though in the initial act the offended was another; in the context of remorse and guilt that offended person is no longer in the picture.
Forgiving is not forgetting either. It is a realization of the fact that there is no future in the past and, therefore, brooding over the past is futile.