Martin Poole was the speaker on the Sunday before Lent which seemed very appropriate given the anti-commercialism embedded in this chapter of Isaiah.
Isaiah urges his readers to focus on the things of true value in life and then you will experience joy. The kind of joy which makes trees clap their hands and and the mountains and hills burst into song.
This is in direct contrast with the popular understanding of Christians who are perceived as judgemental according to a survey conducted recently asking people for the adjective which they think best describes us.
As Christians we are called to joy because God is calling us home to a great celebratory feast.
You can hear his talk here Isaiah 55