The nine-pointed star represents the nine fruits of the Holy Spirit stated in the Epistle to the Galatians in Christian symbolism. The sign might be merely a star, or it can include the Latin initials of all the fruits (Benignitas, Bonitus, Fides, Mansuetudo, Continentia, Charitas, Gaudium, peace, and Longanimitas) inside the star’s points.
The Baha’i Faith considers the number nine to be very significant and a symbol of completion, hence the nine-pointed star symbol is also linked with them.