Sentence examples for sum it up from inspiring English sources

"sum it up" is a perfectly valid expression to use in written English.
The phrase means to succinctly summarize a lengthy topic or speech. You could use the expression in the conclusion of an essay when you want to quickly summarize the main points of the paper. For example, "The story of Romeo and Juliet has profound messages about the power of love and the fragility of life. To sum it up, Shakespeare encourages us to value the beauty of life while making the most of the time we have."