You are a vibration.
Vibration is acted on by cosmic vibration through cosmic force.
When acted upon by force vibration evolves.
That is the essence of Astrology.
There are many metaphysical subjects which are highly questionable when taken too seriously. Astrology is the least so because it has the most physical in nature of the metaphysical topics. I don't, in fact, really consider astrology a metaphysical topic at all in fact. The reasons for this are relatively easy to explain.
When anyone or thing is born the planets, Sun, and Moon are aligned in a very precise way that is determined by a data reading from a chart called an ephemeris. This physical reality is recorded by the thousands of years old tradition of keeping track where celestial objects are related to the constellations which are the background.
The constellations are the signs of the zodiac, a 360 degree wheel where the planets move around the Sun as they orbit it. There are 12 signs associated with certain particular themes of existence based on basic psychological numerology. In this respect, because it is rooted in basic philosophy and advanced psychology, the arguments for astrology are sound.
Beyond this there is a physical understanding of astrology. Everything is a vibration down to its mathematical certainty in creation. Behind the mathematics are the physical structures which surround us at all times, the magnetic fields of the Earth, and the larger and very vast magnetic field of the Sun. These two structures are constantly under the influence of each other. In addition the planets are moving through the Sun's field creating waves in it that are no doubt detected by Earth's magnetic field because of the huge size of these structures.
This is a pattern that is force and energy in combination to produce vibration upon you, another vibration. That is the physical explanation as to why astrology works. However the interpretation of astrology is a matter that is actually entirely debatable for the nature of the field transformation effects of the planets, Sun, and Moon are subject to considerable debate among astrologers. Most astrologers are either too positive or too negative in their interpretations.
What we are most looking for in astrology is the timing of energetics, the proper use of energy at particular times that are least resisted by collective pressures from society and the world. This is what the primary branch of astrology works with when we talk of transits. Transits are caused by the change in position of the planets relative to the time you were born. There are specific energetic triggers caused by geometric alignment that lead to resistance being born especially of sensitive individuals to the shift in position of the systems of cosmic alignment, which are the planets, Sun, and Moon again.
Astrology allows one to analyze the energy of a particular person or situation and guesstimate an outcome based upon the energetics of the person, the place, and the celestial objects. The predictability is high for simple situations and correspondingly lower for complex ones, but the feeling is always the same for those experiencing the situations described by transit astrology. A second form of astrology exists called the progressed school of astrology. This one looks at the internal dynamics a person's soul development as a human. There are additional ways of looking at astrology including vedic, solar return chart, and several other commonly used methods.
What a person needs to know is that astrology gives them information about the best time to do things and the best time to sit back and reserve their energy until a better time. In addition the challenges of life can be prepared for better with astrology as the timing of events are more often then not linked to the emergent property of the astrological situation. This emergent property appears magical but is rooted in basic mathematical synchronicity. Relationship dynamics are similarly governed by another mathematically structured system called synastry. All of this is governed indirectly by the symmetry of coincidence, the mathematical principle behind unexpected events. Thus there is a structure and order to the completion of projects that allows for the flow of energy in accordance to the astrological timing.
How important is this? It depends on what you want to get done. I view the matter as a question of divine timing built into the charts specifically to give credence to the power of those things which are greater than ourselves. Such a reason and logic is a subtlety, something which bespeaks of a sensitive and receptive character. Such people can make the most out of astrology and energetic alignment concepts. People who are more bullish don't have use for astrology, but they run the risk of challenging a will greater than their own in society most often that represents the power of the Sun, Moon, and planets are representatives of cosmic order. Rebels are great till they blow up the grain silo.
This sort of reasoning was never going to have universal appeal in this day and age. But, as we recognize our place in the universe as being sentient and least in importance compared with the bigger picture represented by the celestial objects (really we should call them beings) we take into account the true measure of our humanity. For such a delicate and receptive age to come into being would go far to advancing the cause of consciousness on this Earth. Indeed it is my opinion that Aquarius is the true sign of astrology and as we enter into the Aquarian Age more fully astrology will probably be the only school of thought in the metaphysical arena that will be much tolerated by the atheist majority. As such it can expected to have a strong influence on many societies as we move forwards in time.