Content writers are individuals that write creative contents for websites and organizations. They write professionally based on what the organizatio wants them to write and they are very thoughtful with their choice of words. The goal of a content writer is to keep readers interested in the message they are conveying and spur such readers to read more and take action. A content writer cannot share or promote his/her personal opinion but the opinions of the individual or organization that he/she is writing for. There's no room for sentiment in their write up- everything must be done professionally.
A blogger on the other hand write to entertain or to keep readers hooked. They share their opinions and sentiment in their write up and they decide the flow of the write up. Bloggers share and promote their opinions in an informative or entertaining manner while content writers share and promote the opinion of the individual or organization that they are writing for.