The engagement of Jessica Lynn Christensen and Jacob N. Long is announced today. The future bride is the daughter of Kyle and Glenda Christensen. Parents of the future bridegroom are Mark and Jill Long of Olive Branch, Miss. The wedding is planned for Saturday, Dec. 19, in Nashville. Miss Christensen received a bachelor's degree in marketing from Union University in Jackson, Tenn., where she was a member of Chi Omega sorority. Mr. Long received a bachelor's degree in exercise science from Union University, where he was a member of Alpha Tau Omega fraternity.