There are many kinds of openings: wood, marble, glass, plastic, fabric, strings of beads and more. Doors open and close and slide and flap. They let in the sun and sometimes pets and occasionally creatures of nature. Sometimes they are locked and other times they are open. They are used to protect those inside and keep out the storm or give shade against the heat or stop the cold from entering. 

Questions can sometimes lead to answers but sometimes they lead to more questions. That is what makes various sermons both interesting and entertaining. So, what is a door?