John 3

"29The bride belongs to the bridegroom. The friend who attends the bridegroom waits and listens for him, and is full of joy when he hears the bridegroom's voice. That joy is mine, and it is now complete.
30He must become greater; I must become less."

I think through these verses we could see what struggel John had and to what solution he came. Of course he did know from the very beginnin who he is. When the people, send by the priest, asked him in chapter 2 who he is he testified who he is and which duty is assigned to him. I could imagine that he proudly answered these people that he is doing work for God and that he is chosen by God.

But later disciples of him came to him and complained about Jesus thay may thougth that John is Chirst. On top of that Jesus was even babtized by John. In this case he had really humble himself and told them his position and that he is below Jesus even if he started earlier to be present than Jesus. And he also not only told them not to complain but showed them that it is a joy for him that more and more people are coming to Jesus. I think that this step is one ahead the first of knowing ones duty. Because if he only knows about his duty he might still complain or does not understand. But with this answer it is made clear that he not only know but also understand his role because he is able to convince others about it.
This is like denying oneself and give room for Jesus. As it is said in verse 30 Jesus must become greater; I must become less. This is similar to a hymn we are singing.
But as mentioned before: It is easier to know, than to understand and experience it. Because this is the step where you are active.
How nice would it be if we could be happy when others become stronger especially when it is Jesus in our heart and when he is growing and oneself is not alone anymore.