Paul gives the example of running the race. If all you ever do is cross the start line (i.e accepting Jesus, baptism) and then never actually live out your faith, and bear good fruit, then you might just end up being like the fig tree that Jesus cursed. There are too many folks out there that are “believers” in name only who may talk the talk but don’t walk the walk.
OR, you might be the person Paul refers to as having their wood, hay and stubble burned up by they themselves saved, as by fire. Jesus explained it as simply as possible in His lesson to Nicodemus regarding the brass snake. You are addressing rewards, not a means to salvation.
The fig tree is a symbol, Judaism. The tree was really there and really not bearing any fruit. But it was full of showy limbs and leaves!