קדושים תהיו

I copied this from something I wrote many moooons ago:

What does it mean to be "kadosh" - holy?

Sitting on top of a mountain and meditating?

Fasting every day?

Learning non-stop?

Davening with unbridled intensity? 

Well, when we go under the chuppah we perform "kiddushin"? The root of kiddushin is "kadosh". So what is kiddushin? Tosphos at the beginning of Maseches Kiddushin says that it means "special" or "set aside" [miyuchedes]. Being mekadesh a woman means that we say "You are special to me. There is nobody else." 

Kedusha means that we live our life in such a way that shows that Hashem is special to us, that we are completely dedicated to the relationship. If anything else besides Hashem matters then He is no longer special. 

Kedusha means living in the world - for Hashem.