Sri Chinmoy is a "fully realised" spiritual Master dedicated to inspiring and guiding those seeking spiritual advancement (he also conducts meditations for the United Nations twice each week). "Beyond Within" is Sri Chinmoys' magnum opus in that it details and explains the true path in our spiritual advancement.
I fully recommend all the books written by Sri Chinmoy (his book "Meditation" is also required reading)to a get a deeper understanding of more spiritual topics.