For the oldest Cub Scouts, the Arrow of Light program offers 5th grade Webelos the opportunity to earn a patch that transfers to their Boy Scout uniform. By earning this recognition, a scout demonstrates he is ready for the next step on the boy scout trail.
During their last year in a Pack, Webelos get a larger say in which adventures their den will do, and in leading their fellow scouts, both skills that will come in handy in Boy Scouts.
A boy that is new to Scouting in 5th grade does not need to earn any previous ranks. He can earn the Bobcat badge and then the Arrow of Light along with his den, even if he does not have the Webelos badge yet. If it's important to him, he can put in more effort and fulfill the Webelos requirements during 5th grade also, without missing out on the adventures his den is doing for Arrow of Light.