Knock on Wood!

Everyone has heard the term, "knock on wood!" to keep your good luck. But where and why did it come about?
To start, no one can really trace back the one true origin. There are believe origins for Christians, Jewish people, pagan groups.
It is said that many pagan groups that worshipped trees. The Ancient Celts thought that spirits and gods lived inside the trees. One origin belief is that people would knock on the wood of their houses to scare away evil spirits that could possibly ruin the good luck that the people were discussing. A second idea is that people would put their hands on trees to ask for good luck from the spirits living inside or to show appreciation for the good luck that they have received.
The Christian origin belief is that knocking on wood (the wood of the crucifix) is like asking for protection (from Jesus Christ).
The Jewish origin belief arises during the times that the Jews were being run out and killed during the Spanish Inquisition. Synagogues and Temples were built out of wood. Jewish people would have secret knocks on these Synagogues and Temples in order for the doors to open, and therefore, have their lives saved.
Although we have these many origins, we still cannot say which one is true over which. In fact, the first documented use of "knock on wood" happened only about 100 years ago. So it's hard to say: does "knock on wood"'s origin date back hundreds and hundreds of years ago? Or did this saying just come about?




http://mentalfloss.com/article/50079/why-do-we-knock-wood
http://www.todayifoundout.com/index.php/2014/01/knock-wood/