Buttons: Order of execution

I have a method in in which I have the line:

self.greenButton.configure(text="Loading",state="disabled", 
background="green")

followed by other lines.

Being a complete newbie, I would expect the green button to start 
showing the text "Loading" before execution of the lines following the 
abovementioned line.

But it does so immediately afterwards.

I am not looking for a direct solution, but this shows that I do not 
understand how to write tkinter code involving buttons. Is there a 
simple explanation how to

go about writing code so as to make things happen, either at all, or 
when I want them to happen?

Regards

John Sampson