After spending nine months in a Missouri jail for a crime he did not commit (the shooting of former Gov. Lilburn Boggs), Porter made his way to Nauvoo. He "crashed" Joseph Smith's Christmas party at the Mansion House. No one recognized him. The guards couldn't throw him out so, the Prophet tried to and finally recognized him.
He then asked Porter to tell the story of his capture, imprisonment, and escape to Nauvoo. After the story telling, the Prophet gave Porter a blessing, promising that as long as he was true to his covenants, his God, the Church, and his people "no bullet or blade" would ever kill him. That meant than no man could kill him. As a token of the blessing he was never to cut his hair nor his beard. He was also given the power of healing.
-John W. Rockwell