The glass of the gospel is excellent and eminent above all other glasses. It is a mirror that changes us. When we see ourselves and our corruptions in the glass of the law, we see ourselves dead. The law finds us dead and leaves us dead; it cannot give us any life.
But when we look into the gospel and see the glory of God, the mercy of God, and the gracious promises of the gospel, we are changed into the likeness of Christ, whom we see in the gospel. This excellent glass has a transforming power to make beautiful. Such a glass would be much prized in this proud world; such a glass is the gospel.
Taken from the book Glorious Freedom by Richard Sibbes 1639