One main theme is the worship of God. It emphasizes the importance of adoring God. Another theme is God's power. The hymn shows how powerful God is. Also, there is a theme of God's love and care for His creation.
One connection could be that 'O Holy Night' might have been sung during World War I in the trenches. Soldiers, far from home and in the midst of horror, may have found solace in this holy song. It could have reminded them of the peace and hope that Christmas represents, even in the darkest of times.
According to the information you provided, I am unable to confirm the specific plot you are referring to. If you can provide more background information or context, I will try my best to answer you.
In the novel Lotus Lamp, Chen Xiang was the son of the Three Holy Maidens. The Three Holy Maidens stole the Lotus Lamp to save the world and violated the rules of heaven. They were pressed down at the foot of Mount Hua. In order to save his mother, Chen Xiang worshiped Sun Wukong as his teacher to learn martial arts. After experiencing all kinds of hardships, he finally used the Xuan Hua Divine Axe to split Mount Hua and save his mother from danger.
In the novel, Chen Xiang did not use the demon to plant the Three Holy Maidens. Instead, he relied on his own efforts and courage to finally save his mother.