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The motto is by Seneca the Younger (circa 4 B.C. to 65 A.D.), who was a prominent Roman from a family in Roman Spain or Hispania. His writings on philosophy and his plays have been influential in Western thought and literature. His father, Seneca the Elder, was also prominent, as was his relative, the Roman poet Lucan. A brother of Seneca the Younger was the Roman proconsul Gallio who appears in the New Testament in contact with Paul of Tarsus (see Acts 18:12-17). All in all, a very prominent family and an example of how the Romans drew talent from the far reaches of their realm.
Statue of Seneca the Younger in his native Córdoba, Spain/Hispania
By Sénèque_-_Cordoue.JPG: PRA derivative work: PRA (Sénèque_-_Cordoue.JPG) [CC-BY-SA-3.0 (www.creativecommons.org/licenses/by-sa/3.0) or GFDL (www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons
Translation of the motto: "Long is the journey through precepts [or rules], short and efficacious/powerful [is the journey] through examples."
The motto summarizes the approach of your textbook Lingua Latina.