Nine is the highest digit, hence symbolizes comprehensiveness, culminations; also, the reason it is used in the Temple’s form is because 9 has the exact numerical value of ‘Bahá’ (in the numerology connected with the Arabic alphabet) and ‘Bahá’ is the name of the Revealer of our Faith, Bahá’u’lláh. The 9-pointed star is not a part of the teachings of our Faith, but only used as an emblem representing ‘9‘. In telling people of the 9 religions of the world, that is ‘existing religions, we should not give this as the reason the Temple has nine sides. This may have been an idea of the architect, and a very pleasing idea, which can be mentioned in passing, but the Temple has 9 sides because of the association of 9 with perfection, unity and ‘Bahá‘.
(Shoghi Effendi, Directives from the Guardian, p. 52)
Such suppositions regarding lucky or unlucky numbers are purely imaginary. The superstition concerning thirteen had its origin in the fact that Jesus Christ was surrounded by twelve disciples and that Judas Iscariot was the thirteenth member of their gathering. This is the source of the superstition, but it is purely imaginary. Although Judas was outwardly a disciple, in reality he was not. Twelve is the original number of significance and completion. Jacob had twelve sons from whom descended twelve tribes. The disciples of Jesus were twelve; the Imams of Muhammad were twelve. The zodiacal signs are twelve; the months of the year are twelve, etc.
(‘Abdu’l-Bahá, The Promulgation of Universal Peace, p. 196)
The Master has said that there is a certain amount of truth in Numerology, physiognomy etc. but it is too much exaggerated by those who advocate them.
(Shoghi Effendi, Lights of Guidance, p. 516)
The number nine which in itself is the number of perfection is considered by the Bahá’ís as sacred because it is symbolic of the perfection of the Bahá’í Revelation which constitutes the ninth in the line of existing religions, the latest and fullest Revelation which mankind has ever known.
(Shoghi Effendi, Lights of Guidance, p. 414)
There is nothing in the teachings which leads us to believe numerology or astrology are needed by the believers to guide them in any way.
(Shoghi Effendi, Spiritualism, Psychic Phenomena and Related Subjects, p. 3)
...it is absolutely essential that the teachings should not be confused with the obscure ideas related to numerology … and the like. Individuals interested in them are free to believe in and credit such ideas and to make any inferences and deductions they desire from them, but under no circumstances are they expected to identify them with the principles and teachings of the Cause.
(Shoghi Effendi, Spiritualism, Reincarnation and Related Subjects, pp. 9, 10)