The crossed keys are a symbol of the Papacy. This is because Christ said to St. Peter that he would give him the 'keys of the kingdom' and that whatever he bound on earth, would be bound in heaven, and whatever he loosed on earth, would be loosed in heaven. (Matthew 16,19). St. Peter was the first Pope and those who have followed share this power of the keys to bind and loose.
The stained glass windows of St. Joseph are just marvelous. They are so eye catching that I almost missed the medallions at the top. This one caught my eye because of the added symbolism in the keys themselves. If anyone can shed some light on the subject please leave a comment.
Picture taken St. Joseph Catholic Church, St. Joseph, Ohio.