In her speech My stroke of insight, the neurophysiologist Jill Bolte Taylor funnily describes her sudden insight into Oneness. The suddenness of her insight is due to the sudden stroke.
It is given to some to realize Oneness due to an extreme situation, however, the sudden insight of the most of us is based on the structure of focus, which is a matter of the gradual process of developing our ability to focus, and if we are talking about the ability to focus, the method of meditation for me personally represents the most effective training of it.
The essence of the meditation is the simultaneousness of focusing (on a specific spot on, in the body or outside of it) AND observing. The detachment from everything that is not, what the essence of the focus is, is the method’s inherent component; as such it manifests by itself and thus needs no conscious or additional search.