In spite of the diversity of the New Testament writings, is there one main theme that unites all the books of the New Testament? If so, what is it?

In spite of the diversity of the New Testament writings, is there one main theme that unites all the books of the New Testament? If so, what is it? Can you state it in one concise and powerful sentence? Provide scriptural support to demonstrate the validity of your answer, and draw on secondary sources as well to strengthen your post