The 9th house corresponds to a fire sign and is therefore a house of dharma (duty or life purpose).
Luck, fortune, father, religion, philosophy, faith, wisdom, worship, guru, grandchildren, long journeys, travel, law, higher knowledge of all kinds, the knees.
The 9th house, being a trikona (trinal house), is auspicious and benefits all its associations. It is on a par with the 1st house in importance because it indicates a person's luck or fortune. If the horoscope reveals strong luck, there will be a solution to almost any problem. Therefore the 9th house should be considered in every judgement. Bhagya bhava also rules religion and philosophy, but one must also check the 8th and 12th houses, Jupiter, and Saturn. If only the 9th is considered, then nearly all powerful or famous figures will be judged as religious, when the indications may simply be revealing the luck which has propelled them to their high platform. Ignore the house of luck and many conclusions will be off the mark.
Note that the 9th rules the father, as opposed to the 10th in Western astrology.
The karakas, or indicators, of the 9th house are Jupiter and the Sun.
The retrograde owner of the 9th house speaks of karmic relationships with the guru and father, of a person’s indecision in comprehending the Highest truths, his doubts about this. It can also give a peculiar understanding of religion, an unusual approach to it.
Source: «Ancient Hindu Astrology for the Modern Western Astrologer» by James Braha