Once you know a thing's name, you control it

an oversimplification of the power that comes from understanding something. once you can identify not only the thing, but the causes, the ramifications, the parallels, you can predict ahead of time what its impact will be. you can even make it serve you, if it's something you can gain from.

in the history of human mythology, there are many stories of deities and saints who create things by speaking their names. philosophers and scientists make us understand things we were subliminally aware of by spelling them out.

it's a sort of wizardry, to know a thing so well that you own it.

This is true in Judeo/Christian traditions. In the OT, when Moses asked who God was, the reply was: "I Am who I Am." A more pure translation is: "I Am who I will Be." Hence, God will not allow His Holy Name to be uttered by any as this control of knowing ones name, of calling them and having them respond to you because you called, is researved only for God Himself. Yahweh, is most often quoted as the true name of God, and in Orthodox Jewish circles, this word is spelled without the vowels thus never actually writing the Holy Name. Whether or not God's true name has ever been uttered, or that He actually has a name is beyond us, but it is indeed held that it is Holy, Powerful and not to be used in vain. Hence the Second Commandment:
"Thou shalt not take the name of the Lord thy God in vain: for the Lord will not hold him guiltless that shall take the name of the Lord his God in vain."