Alma 59

Alma 59:9

"And now as Moroni had supposed that there should be men sent to the city of Nephihah, to the assistance of the people to maintain that city, and knowing that it was easier to keep the city from falling into the hands of the Lamanites that to retake it from them, he supposed that they would easily maintain that city."

Moroni understood that it was easier to maintain a city than to regain it.  The same goes for life.  It is so much easier to remain on the straight and narrow than to fall away and try to come back.  The risk of becoming lost and possibly not finding the light is too high.  It is so much better and easier to remain faithful to the gospel, to pray and study everyday so that the Holy Ghost remains with you and guides you in the right way.