Is the main purpose of religion being decent?
The main purpose of religion is to guarantee that man should serve no one but the one and only God. “Serving no one but the God” means for the man, who is created as a free individual, to live in harmony with his creation.
Allah the Almighty commands:
“Set your face steadily to that religion, the fitra of Allah, in which He has created the mankind. There is nothing to replace the creation of Allah. That is the righteous religion, but most people do not know it.” (30:30)
The one who follow this religion will be in harmony with his creation and therefore, be very decent indeed. The best examples are messengers of God.
Allah the Almighty commands about Muhammad:
“Indeed, you are of a great decency.” (68:4)
Aisha, the wife of the messenger said that the messenger of God had the morality of Quran. (Muslim, Salat al-Musafirin, 139/746)
We also advise you to see the link below; about Morals:
 Fitra is the body of laws that all beings are created, changed and developed according to.