The first word you read in this article is 'Religion', it is at the top of the page and it tells the area of the newspaper, the argument you are reading about.
then you read the heading and below the subheading: 'An important mission' is the heading and it has to attract the attention of the reader who has to be curios to go on reading the article; 'the arrival of Christianity in Great Britain' is the subheading whose function is to give more information about the content of the article and to give information to understand the title.
the function of the paragraphs:
1. tell when Christianity comes into Great Britain
2. introduce the impact of a monotheistc religion in a Country where people have a politheistc religion
3. explain how Christianity could merge with a politheistic culture
4. how the evalengization of Great Briain took place
5. tell who evangelised Great Britain and how they did it
6. the last paragraph is the conclusion