Hi, I’m an English major and both literary works mentioned here were included in my studies.
Based on my studies, my professors told me that the authors at that time were concerned of Protestant reformations and were positive about them in Britain. Both authors did not object to this change. The author of The Pilgrims Progress was a Protestant preacher who disagreed with the Catholic Church, thus writing a religious allegory about this.
However, with Paradise Lost, it’s one of the greatest epic poems you can find. It does have some anti-Catholic motifs in this poem, but it’s really valued for its literary styles and imagery. Please keep in mind that the events happening in the poem are not based strictly from Biblical accounts. Some fictional elements are added. Therefore, it’s not classified as Christian allegory because it has some fictional accounts.
It’s a great read for its literary style and for the admiration of 17th century literature, but not for its theology that it is presenting.