The Christmas carol ‘Joy to the World’, by Isaac Watts, is derived from Psalm 98 in the Bible. This carol, interesting enough is filled with direct references to Christ and his life. ‘Joy to the World’ is referring to the end of the age during Christ’s triumphant return. Some also refer to this as Isaac using ‘Joy to the World’ to symbolize Christ’s actual birth in Bethlehem. Isaac also included, “Let earth receive her king”. Of course, her refers to the earth, however, it also refers to the mother, Mary.
Many have different opinions/belief to the question, why would jesus come to earth as a baby? However, I believe jesus did this because he wanted to prove that he was a mortal like every single one of us.