Colossians 1:6b

that has come to you. In the same way, the gospel is bearing fruit and growing throughout the whole world—just as it has been doing among you since the day you heard it and truly understood God’s grace.

(v6, NIV)

This growing that occurs in these people as well as in the whole world originates from hearing and truly understanding God's grace. Paul talks about the bearing and growing fruit with regards to the world and compares it to the same work done in those he's writing to. So it begins from hearing and truly understanding God's grace. It's interesting how some people just get it and some people don't. Do you understand it? Now, there is a way in which we'll never fully understand, but there is a way in which to some degree we do understand. There is a light that goes on in our understanding, but there is also growing in our knowledge and understanding. This occurs in both these people and people all over the world. It really is quite amazing and joy producing to hear of how it's spreading and to see it occurring in others all over the world.