First we must understand that Anselm believed that faith and reason are two sources of human knowledge. Faith must be that starting point in the search for truth. "For I do not seek to understand in order that I may believe, but I believe in order that I may understand." .
The concept of fittingness as a philosophical criterion basically states that if something makes so much sense and seems to be perfect, and cannot proved otherwise, then it is true. When we keep in mind the quote given to us, "If a thing must be and if can be, then it is." Then we must also keep in mind the question presented to Anselm which is: For what reason or necessity did God become man and by his death restore life to the world, when he could have done this through any other person, or by sheer act of will? .
The reply to this question is, it was necessary for God to redeem man for his sins in the way he did. When we say necessary we mean it needed to be. So, if in fact man needed to be saved, then for Anselm it must have been done this way, according to the picture, for it is the best and most fitting way for God to have saved man. .
For Anselm the question for the nature of mans happiness, or eternal happiness with God, is illustrated in the picture or the scripture that is given to us. The picture is not only fitting for Anselm, but it is appropriate and above all it is perfect. If something is necessary, fitting, appropriate and perfect, then why not believed it.
This concept proves that either by faith or not, the story has no imperfections and by reason we can conclude that God acted in the way he did, by become a Man-God and taking on the lowest form of human nature, born of a woman and died, because it was the best and most fitting way to save man from sin and reconcile man for debt the man could not repay. Furthermore, it would be unfitting for God to show or reveal to man a happiness that could not be achieved by man due to the inability for man to repay his debt to God because of a lack of intellect.