The three important tenets of Buddhism is to know that mind and matter are all 1.Impermanent 2.suffering and 3.Non-self To meditate means to meditate on mind and matter and be aware of it. The difficulty with the meditator here is they try to meditate on concepts of impermanence, suffering and non-self. Concepts don't exist. Take Seeing for example. In the beginning, there is no seeing, but if the eye is good, the object comes up, there is light and your attention is drawn to it. If these four conditions concur, then there is seeing. Once it has arisen, then it passes away. So we say, seeing is impermanent. Since the meditator is watching every arising, all things mental and material appear to him as separate,broken pieces. He is no longer illusioned.
The words are said two times in a row because repeating the mental noting is the technique. So you repeat for example, 'seeing, seeing' not just two times in a row, but for however long it arises.
You may also even repeat the noting 3 times so that you are really observing the object from the beginning until the very end. For example you observe the rising from the beginning until the end by noting "rising, rising, rising" and so on.
