What is the ruling on writing a novel that includes the celebration of Christian holidays as events within the novel without glorifying them, and what is the ruling on saying "go to hell" and "for God's sake"?

As for the phrase "go to hell," it is one of the well-known expressions of the disbelievers, and it may mean the fire of the Hereafter or destruction in this world. It is not permissible to inform or bear witness for anyone regarding Paradise or Hell, except for those whose death upon disbelief has been established, or concerning whom a sacred text has been revealed.

As for the phrase "by God's right" (بحق الله), it is either for causality or for swearing. If the intent of the question is by what is due to God from attributes such as greatness and majesty, then it is permissible. If the intent is swearing, it is better to avoid it to steer clear of disagreement, as some scholars have prohibited swearing by it, because "God's right" (حق الله) is an action of the created being. Others consider it a permissible oath if it refers to God's inherent attributes, such as His greatness and majesty, and they rule that expiation is required if one breaks it.