Why sitting meditation, and is vippasana and breath meditation sufficient? Why do we have to watch body sensations separately by sitting meditation, when even in our daily life we are experiencing sensations moment to moment (and realizing everything is vibrating in our body)?

And can we achieve omniscience and knowledge of our past lives, karma, etc., by watching breath and watching body sensations only? Or there is more to it in vippasana meditations, other than watching breath and body sensations?



(This question was originally titled "tibetan buddhism chanting om mani padme hum and watching the breath meditations and watching mental states")
Breath meditation, vipassana and Samadhi meditation are two sides of the coin. Breath meditation is about focused attention that quiets the mind of chatter and noise. It's as if you let a muddy pool settle after stirring it up. Once the mud (chatter) has settled, the water (mind) becomes clear and can now focus more easily and powerfully than before. 

Now that's all well and good but what do you do with this focused mind? You point it towards the three marks of existence, and/or the four noble truths. While breath meditation is sufficient as a vehicle to carry you into higher states of concentration (the jhanas) if it is not coupled with insight meditation or some sort of reflection then all you will be doing is building up your concentration faculties without reflection or thought.

There is a section in the Visuddhi margaya that talks about reflecting after exiting the jhanas that is essential to jhanic meditation. I'm at work now but can find the reference later today.