The word Kedoshim means "to be holy". The kabbalists speak about the difference between holy and pure. According to Rashi, one of the great commentators of the Talmud, in order for one to be pure, it doesn't matter what we are thinking – as long as our actions are positive.
The word "holiness", however, applies to our actions as well as our thoughts. If a person detaches himself from physical temptations and negative thoughts, he can achieve purity. But how is it possible for us, as human beings, to detach ourselves from all of the temptations this world has to offer?
The explanation is that each and every one of us was born with innate holiness, a superior soul that helps us connect to a more spiritual life. In order for us to be able to "be holy", the word Kedoshim is actually a tool there for us, a tool used to put up safeguards in our spiritual work. For example, when – in our physical lives – we build a house, we build a barrier around the roof to keep anyone from falling off, even though the odds people will be walking on our roof are very small. The same principle applies in spirituality: if we use the kabbalistic tools we were given to safeguard ourselves from the negative, physical temptations all around us, we can achieve holiness in our life.