Source: Youth and Morals, by Mousawi Lari. p. 38-40.
We all know that one of the most important factors of Islam’s advancement was the perfect conduct of tile Prophet (S.A.W.). This fact is stated in the Holy Qur`an where Allah, the Almighty, says:
“And had you been rough, hard hearted they would certainly have dispersed from around you.”Qur`an 3:158
The Prophet of Allah (S.A.W.) treated all people equally. His deep and indescribable love for humanity was perfectly manifested in his angelic being. He attended to all Muslims’ needs equally.
“And the Messenger of Allah (S.A.W.) divided his moments between his companions: he would attend to this and attend to that equally.’’
Rawdah al-Kafi .p.268

He also condemned ill nature; he repeatedly said:
“Ill nature is evil and the worst of you are those who are ill-natured.”
Nahj a1-Fasahah, p.371
and:
“0 sons of Abdul Muttalib. surely you will not (he able to) satisfy people with your money, therefore meet them with cheerful faces and joyful conduct.”

Wasail ash-shia v.2, p. 222
Anas ibn Malik. the Prophet’s servant, used to say when he remembered his (the Prophets) excellent traits:
“I have served the Prophet (SAW.) for ten years; during this time he has never said ‘woe’ (as if complaining) to me, regardless of what I did or did not do.”
Fada’il aI-Khamsahv.1. p. 119

Furthermore, good conduct and cheerfulness are factors which prolong life. Imam Sadiq (A.S.) said in this regard:
“Kindness and good manners make land flourish and prolong lives.”
Wasã’il ash-Shia, v.2, P. 221.

Dr. Sanderson has written this on the subject:
“Kindness is an important factor in treating and preventing Illnesses. Most medications result in unwanted side—effects along with a temporary cure, while kindness causes everlasting cures to all parts of the body...kindness moves all powers of the body. Blood circulation in those who enjoy good manners is excellent, and their breathing is better...”
Pirozi Fikr

There is a beautiful point in Imam Sadiq’s statement. He (A.S.) says there is a direct relationship between kindness and good manners and stated that they are among the factors which prolong life. The reason behind this is that kind people enjoy a sense of happiness and satisfaction, thus, both kindness and good manners have the same desired effects. Imam Sadiq (A.S.) also considered these traits elements for achieving happiness when he said:
“Part of man’s happiness is his good manners.
Musadrak a/-Wasail V..2, p.83
Samuel Smiles added on the same topic:
“Good manners and emotional balance have their effects on man’s development and happiness just like other powers and Instincts do. As a matter of fact, individual’s happiness is greatly related to their affections and good manners.”
Akhlaq.
In addition, good manners make life easier and increase subsistence and harmony, Imam Ali (A.S.) said:
“Good manners bestow subsistence lavishly and make friends (more) intimate.”
Ghurar al-Hikam p. 279
S. Marden wrote the following in his book:
I know a restaurant manager who became very wealthy and popular because of his good conduct. I learned that travelers and tourists traveled long distances to reach his restaurant; they did so because in this restaurant they liked the privacy and the pleasant atmosphere. When the customers are at the restaurant, the said manager cheerfully greets them in a manner that is not duplicated anywhere. In fact, in this restaurant they do not experience the cold nuisance complaints that you find in other restaurants. In this restaurant the employees try to show affection and build friendly relationships with the customers, instead of the usual seller—buyer relationships. The employees smile a lot and give special attention to serving their customers,this attention stems from love and affection for their guests. The employees establish such relationships with their guests that the guests not only feel that they should come back but also bring their friends. It is clear how effective this method is in attracting new customers”
He added:
“Good Manners have not played a more important role throughout history than at this time. They have become the capital of those who wish to bring happiness and success to their lives