Do you know the bit where Paul says that Timothy learned the gospel from him, but also from his mum and grandma. People invested in Timothy. And then Paul tells Timothy to do the same to pass the gospel on. That is the meaning of real discipleship, you know you are growing when you are passing it on. Again something we cannot do as isolated individuals.
Growth is a process.
Peter wants people to grow. And this too is in the church, because he will go on to say that we need to be mature to spot false teachers in the body. Notice that all the things he mentions are to do with our characters, not with our skills. Finally growth requires commitment and time. It doesn t just happen.