The phrase "great motto" refers to a powerful or inspiring statement that represents a person or a group's values or beliefs, and acts as a guiding principle for them. Full definition
«Jack Stack [president of Springfield Remanufacturing Corp. and an early proponent of open - book management] has this great motto of sharing his kingdom with everyone,» says Grossman. (inc.com)
The great motto of Origen of Alexandria was, «Be diligent in reading divine Scripture, knock, it shall open unto you». (religion-online.org)