The Scotland you live in today has been shaped by events in history. And many of these events also created the roots of sectarianism.
In the 1800's and as land ownership changed, Scottish industries developed, people flocked to new communities around the mines and factories. People naturally clustered into protestant and catholic communities within villages, towns and cities - even down to the street they lived in. The arrival of Irish immigrants to supply essential labour created not only new communities but resentment from local people.
History has also played a part in the types of jobs available to people and their social lives and contacts, depending on their religion or background. Many organisations, associations, clubs and sports activities grew out of the communities described above and are always associated with them. This is not accurate, but it does happen.