This has the potential to be a very long answer but I will try to be brief :) Structure is intertwined with function. Often, structure is what determines or enables function and this applies to molecules, macromolecules, and all the way up to organisms. If the structure of something is changed, often the function is too. One prime example of this is in proteins. This is why when they are denatured (their shape changes) they no longer function correctly.