You may want to ask your instructor for clarification, too, if that's an option, but I'll gladly give you my sense of how to think about crafting a good answer. The question asks you to write a “critical note,” which is very different from what I normally think of when I hear the word “describe.” “Describe” seems to me much the same as summarize, whereas “a critical note” seems to ask for less summary and more analysis.

In writing your answer, you can assume that your reader already has a general familiarity with the works that you are going to discuss. You can refer to them by name, perhaps give a one-sentence summary, and then quickly zero in how you view the treatment of religion in several, most, or all of the named works. (If the question does not specify number of works that you have to discuss, consider discussing at least three works in detail. Consider focusing on works that have something in common but that also show a range of attitudes toward Christianity, if that is possible.)

Here’s a brief quotation from one of the enotes study guides that may interest you:

One perhaps detects in the speaker’s words a deeper longing for a wilder, more exhilarating time before the “civilization” brought by Christendom. Despite the poem’s overt appeals to a Christian God, the memory of pagan heroism haunts “The Seafarer” with elegiac longing and explains why the speaker of the poem would seek out the pain and danger of seafaring as an alternative to the more settled life of the town.

This passage could be called a short critical note. It contains some summary or description (e.g. “the poem’s overt appeals to a Christian God”) but moves quickly from that surface observation to a richer or deeper analysis.

What is really good about this passage from the enotes study guide on :The Seafarer" is that it discusses the tension between belief systems, something that is certainly found in the epic Beowulf, in the illustrations on the Franks Casket, and probably in a good number of the works that you are being asked to look at. Perhaps that idea of tension between belief systems (the old and the new) could be the central theme of your critical note.

I hope that this reply is helpful.