Vaastushastra as we all know is an ancient Indian architectural science. It contains principles to ensure a harmonious balance between man & nature thereby bringing happiness, health, wealth & prosperity. However as an Architect I see how people now have started practicing vastu more as a superstition rather than as a logical ancient science which is relevant to the modern world in a limited capacity.
Vaastushastra originated thousands of years ago in ancient India. In those days people were dependent on the elements of nature to fulfill all their basic needs. Sun provided light & heat, wind gave cool breeze, rivers & rain were the main source of water, earth provided food & shelter and fire heat & protection. Thus the principles of the building science laid down during those days too were based purely on the effect of elements of nature. In the age when it was formulated, the society was largely illiterate, the illiteracy generating a fear of the unknown. Science was beyond the realm of their understanding while religion was omnipresent. It was therefore simpler for the ancient Vastu experts to spread the concepts of the Vastu Shastra through the intricate network of religion and superstition. Unfortunately, as time passed only the superstition filtered down the generations, while the actual theory eluded the world.
All the ancient doctrines of Vastu Shastra may not be applicable in the present scenario in their entirety. Some of the tenets particularly show a strong social bias, which was relevant to the social structure which existed at that time. Such tenets have certainly lost their significance now. However the fundamentals of the vastu theory are still relevant & can be adapted to the modern world.
What we need to keep in mind is to recognize it as a logical science which has nothing to do with religion. It is true that over the years Vastu Shastra has imbibed religious overtones, but that does not seem to have been the original idea. The religious implications were probably inculcated by the proponents of the science, when they realized that the society of that time, being a God-fearing one, would not accept norms that strayed away from the notions of God.
To understand Vaastu all one needs is a little knowledge about Astronomy. For example we know that our earth, while moving around the sun, continues to spin on its own axis with a tilt of 23.5 degrees. While spinning, the earth moves from West to East. You will observe that car is designed in such a way that its front part is kept lower than the rear part, to enable it to overcome the wind resistance when in speed. Similarly the nose part of the plane and rocket are kept tapering forward. Since our earth is moving from West to East, if your building is lower on the East and higher on the West, only then it will be able to withstand the resistance of winds easily and get filled with positive energy from North-East, leading to peace and prosperity of the inhabitants. Similarly the Sun, as our ancestors revealed, is the only source of light and heat for human and other living beings. It directs and sustains life on earth. Therefore, the rising Sun is like God, and its direction of rising is considered pious and is taken as a point of reference. Therefore, the effect of the direction affects the building / house constructed therein. Thus a clear understanding of the principles of science can help you to delve into the true meaning of Vastu Shastra.
It is a fact that the original Vastu tenets prescribed the type of site and then specified the layout materials and construction techniques and directions. In an urban milieu, one can hardly indulge in choosing dwelling sites or for that matter direction of choice. (I myself live in an apartment in a building, both of which hardly confirm to most of the rules of vastu but still without being immodest I can say I am healthier & wealthier than many of my clients whom I mentioned earlier) .We should look at adapting macro level implications of vastu to contemporary needs logically not superstitiously.
Vastu Shastra can not be directly linked with prosperity. It only suggests ways in which we can live in tune with the laws of nature so that we can be healthy and peaceful and work efficiently. The ancient texts of Vastu Shastra have probably claimed to bring prosperity, as an indirect consequence of being able to perform well at home and work.
I would like to emphasize that however God-fearing you may be, you should not feel threatened by Vastu Shastra because it is a science. Science does not condemn God, or disprove its identity. Vastu Shastra is the science of structure, formulated to help us live in tune with nature. It does not give solutions to your domestic or financial problems.
Vaastu Shastra evolved as a compilation of planning principles for a healthy living based on the knowledge base of the time (similar to Western treatises such as Vitruvius') and was not meant to be absolute. In recent years, it has again gained mainstream popularity, and there are several Vastu 'consultants' in India, some dubious, some genuine. Unfortunately, again many of the modern Vastu exponents are exploiting the layman ignorance and gullibility.