Answer by taking a quote from the following article:

Matthew Paris, known as Matthew of Paris (Latin: Matthaeus Parisiensis, lit. "Matthew the Parisian"; c. 1200 - 1259), was a Benedictine monk, English chronicler, artist in illuminated manuscripts and cartographer, based at St Albans Abbey in Hertfordshire. He wrote a number of works, mostly historical, which he scribed and illuminated himself, typically in drawings partly coloured with watercolour washes, sometimes called "tinted drawings". Some were written in Latin, some in Anglo-Norman or French verse.

From 1235, the point at which Wendover dropped his pen, Paris continued the history on the plan which his predecessors had followed. He derived much of his information from the letters of important people, which he sometimes inserts, but much more from conversation with the eyewitnesses of events. Among his informants were Richard, Earl of Cornwall and King Henry III, with whom he appears to have been on intimate terms.  The king knew that Paris was writing a history, and wanted it to be as exact as possible. In 1257, in the course of a week's visit to St Albans, Henry kept the chronicler beside him night and day, "and guided my pen," says Paris, "with much goodwill and diligence." It is curious that the Chronica majora gives so unfavourable an account of the king's policy. Henry Richards Luard supposes that Paris never intended his work to be read in its present form. Many passages of the autograph have written next to them, the note offendiculum, which shows that the writer understood the danger which he ran. On the other hand, unexpurgated copies were made in Paris's lifetime. Although the offending passages are duly omitted or softened in his abridgment of his longer work, the Historia Anglorum (written about 1253), Paris's real feelings must have been an open secret. There is no ground for the old theory that he was an official historiographer.  Naturalists have praised his descriptions of the English wildlife of his time, brief though they are: in particular his valuable description of the first irruption into England in 1254 of the common crossbill.

was being a historian related to the church
The king knew that Paris was writing a history, and wanted it to be as exact as possible. In 1257, in the course of a week's visit to St Albans,