In this story Sir Gawain and the Green Knight there are many aspects which involve realism, supernatural, and religious sentiment. Realism meaning things that are real life like things. Supernatural meaning magical or unreal. Religious sentiment means things that have to do with religion. All these aspects make the story Sir Gawain and the Green Knight the great story that it is. Some examples of realism in this story are things that could happen at any time and age and they are possible.
In the beginning of the story King Arthur happens to be celebrating New Years Eve, Sir Gawain is part of that celebration. A battle or fight takes place that involves Sir Gawain and the Green Knight. All of these things are possible. The supernatural things that take place in this story are magic of some sort. The Green Knight and his green horse are both impossibilities, it just doesn't happen. "There were stares on all sides as the stranger spoke, for much did they marvel what it might mean that a horseman and a horse could have such a hue, grow green as grass and greener it seemed." All of the people at King Arthur's celebration could not believe their eyes when they saw the Green Knight and his green horse.
The religion in this story is at a minimal amount, meaning there isn't much of. During one of the fights Sir Gawain prays to God to save his life. "Let God work! Ah me! All hope of help has fled forfeit my life may be but noise I do not dread." God saves Sir Gawain from his untimely death. Sir Gawain left the fight with only a scratch.
Sir Gawain and the Green Knight blends all three aspects realism, the supernatural and religious sentiment. This story needs all three key elements. With out realism, the supernatural, and religious sentiment this story would be dull and boring.