Why did Mary wrap Jesus in swaddling clothes and lay him in a manger?

The scripture at Luke 2:7 says that Mary "brought forth her firstborn son, and wrapped him in swaddling clothes, and laid him in a manger..."(KJV)

"Swaddling" has been the custom in this area for centuries. A mother tightly wraps the baby in swaddling clothes (or cloth bands) when it's time for sleep, and it helps them to feel secure and go to sleep quickly. It gives the baby an almost mummy-like appearance as it keeps the baby's body warm and straight; It also helps the child learn to breath through it's nose, by putting bands under the chin and around the head. Mary then placed Jesus in the 'manger' to sleep because it was the softest, cleanest part of the stable where they were staying, since there was no room for them at the inn. (Luke 2:7&12)