Ans : A ladder to climb onto complete islam, just like wazu is a ladder for namaz and walking to masjid is ladder to enter masjid for namaz.
you wash ur body parts and you get reward, you walk and you get reward.
Because you are doing that things to fulfill the command of Allah.
With out intention of namaz, if you walk upto masjid you dont get any reward, because your walking is not to fulfill the command.
Similarly your tabligh will fetch you reward only when you fulfill the commands of Allah, and if u dont fulfill the commands then you going in tabligh is not more than a roaming on roads and
in words of colonel Amiruddin
if your not fulfilling the command of Allah then you are just like a dead body(burden) over the shoulders of soldiers in the war.