Why are there Chinese characters with Unihan code but do not have a definition?

Sometimes I may randomly draw a Chinese character out on the iphone and it matches an existing character, but why is it that when I search it, it doesn't have a definition. I try looking in the unicode databases but still there's no definition and sometimes no pronunciation. Is it because the character's are too old that there's no definition or what. Why would they have a character without meaning?

For we did not follow cleverly devised myths when we made known to you the power and coming of our Lord Jesus Christ, but we were eyewitnesses of his majesty. For when he received honor and glory from God the Father and the voice was borne to him by the Majestic Glory, "This is my beloved Son, with whom I'm well pleased," we heard this voice borne from heaven, for we were with him on the holy mountain. And we have the prophetic word made more sure. You will do well to pay attention to this as to a lamp shining in a dark place, until the day dawns and the morning star rises in your hearts.