Sometimes listening to God requires great silence so we hear what God is saying through all the din of life. Other times we do hear what God is saying, and the difficulty in listening lies in the struggle to execute what he is saying. While filling jars with water may not have been too physically difficult, I wonder what the servers were thinking. They were probably thinking that the order was quite counterintuitive, since they needed to get more wine but were being told to fill the jars with water. So the difficulty in listening to Jesus, for them, was in believing that whatever he tells them to do is going to produce more wine.
Oftentimes, the hardest part in listening to God is the faith part, having faith that what he tells us to do will actually help us achieve what we seek to achieve. Faith produces obedience. If we do not have faith in someone or something, we will find it hard to obey them. With faith in Christ comes great strength, because in being obedient to him his power works through us. When the time comes, will we have the strength of obedience to listen and do whatever Jesus tells us?