For millennia, Vedic astrology has been an oral tradition. Masters transmitted their Jyotish wisdom to their disciples verbally; which has been the only way to learn Vedic astrology. Most of the teachings were never written down. Disciples memorized each verse spoken to them, so that they, in turn, could pass the wisdom to their students.
In order to have access to the living, breathing truth and wisdom of Jyotish, one had to be accepted by a Vedic master into the Sampradaya [a lineage of masters, with teachings handed down from generation to generation].
It has always been impossible to gain access to the teachings of the Jyotishis solely through the few classical texts.
In fact, there were (and still are) many problems with Vedic astrological texts, including major mistranslations, books written by those who never spent any (or enough) time under the tutelage of a Jyotish master, etc. But the primary issue remains that the classical texts were never written to be read by themselves. Each verse was written with the understanding that it would be unfolded and clarified by one's Vedic teacher.
For example, in Chapter 15, verse 4 of the Brihat Parashara Hora Shastra -- which I chose at random -- states:
Housing Comforts: If the 10th lord joins the 4th lord in an angle or in a trine, the native will acquire beautiful mansions.
From this shloka, one might incorrectly infer that when two Kendra lords combine, a yoga automatically forms. But, as I was taught by my Jyotish guru Hart deFouw, one can only truly understand classical verses by examining them in the context of each of the 12 Lagnas. What one discovers is that for 10 of the 12 Lagnas, the joining of the 4th and 10th lords create Raja Yogas (as shown above via the highlighted houses ruled by each). It is the Raja Yogas formed that enhance the 4th house themes.
Another insight is that the enhancement of 4th house themes only occurs if the planets are very well-placed (in a Kendra or Trikona). Also implied here, to the student reading (or listening) carefully, is that yogas enhance not only the house occupied by the yoga-forming planets, but also the (other) houses ruled by them. All of this in one short verse.
This illustrates that each shloka in Vedic texts can only be fully comprehended by working examples, which is one of the many teachings that Jyotish gurus share with their students.
Sadly, much has been written about Jyotish by those without true knowledge. Without meaning to, they vitiate the material and harm the tradition.
"A deaf man passed by a hall where a wedding reception was being celebrated. When he looked through the window, he saw people engaged in exultant and tumultuous dancing. But because he could not hear the music, he assumed they were mad."
This quote, of a Hasidic story from here, illustrates this issue.
I, myself, tried to learn Vedic astrology at first from books, and although I am a bright and diligent student, I failed completely. It was not until I became a student of Hart deFouw that I realized what it meant to be part of a lineage, and to have the magic of Jyotish come alive.
When one is immersed in the tradition, it becomes clear that the issues raised by those ignorant of Jyotish -- e.g. postulating using the Tropical Zodiac, trying to invalidate classical principles, and blending Western and Vedic methods randomly -- carry no validity at all.
You can't learn Vedic astrology well without being part of a lineage.
I hope that all of us can learn to cherish the incredibly rich and alive wisdom that has been so carefully preserved and passed down to us. And that by exploring what is present in Jyotish, we can come to realize the blessings we have.