When we receive pointing-out instructions from our root teacher, we are being introduced directly and nakedly to the reality of mind's nature. These instructions become very effective if we have prepared ourselves to receive them.
...Pointing-out is similar to pointing to the sky when it is very cloudy and saying to someone, "There is the blue sky." The person will look up and say, "Where?" You may reply, "It is there, behind the clouds." The person to whom you are pointing out the blue sky will not see it at first. However, if even a patch of blue sky appears, then you can say, "Look--the blue sky is like that." The person then gets a direct experience. He or she knows experientially that there is blue sky, which will be fully visible when the clouds are gone.
--from Mind Beyond Death, by the Dzogchen Ponlop Rinpoche