People of Eorzea can adopt a patron deity for any number of reasons. Be they personal, familial, or otherwise.
A great example are the Ala Mhigans, who for many decades took Rhalgr as their patron deity. This was inspired by the religious Order of the Fists of Rhalgr joining the city-state. Five years before the fall of Ala Mhigo, however, the King of Ruin - feeling threatened by the Fists of Rhaglr - outlawed the worship of Rhalgr and claimed that he was chosen to rule by divine right of Nymeia, which forced radical changes upon the city-state. Was the King of Ruin truly blessed by Nymeia? Probably not.
Likewise, Ishgard chose to worship Halone because, according to the Enchiridion, their holy book, Halone came before Thordan and chose the Ishgardians as her people, later lending her own power to Haldrath in defeating Nidhogg. So the legend goes anyways.
But one can choose to take a patron deity for a reason as simple as it coinciding with their birthdate, similar to how we view the Western and Eastern Zodiacs.
A crafter may also choose to worship Byregot, the Builder. A thaumaturge, Nald'thal. A wealthy man, Nald specifically. A wandering minstrel may choose to walk the path of Oschon. Perhaps you choose to worship all twelve, or none at all. It varies person by person and for whatever reason truthfully.
There's no solid lore on why patron deities are chosen person by person though.
A great example are the Ala Mhigans, who for many decades took Rhalgr as their patron deity. This was inspired by the religious Order of the Fists of Rhalgr joining the city-state. Five years before the fall of Ala Mhigo, however, the King of Ruin - feeling threatened by the Fists of Rhaglr - outlawed the worship of Rhalgr and claimed that he was chosen to rule by divine right of Nymeia, which forced radical changes upon the city-state. Was the King of Ruin truly blessed by Nymeia? Probably not.
Likewise, Ishgard chose to worship Halone because, according to the Enchiridion, their holy book, Halone came before Thordan and chose the Ishgardians as her people, later lending her own power to Haldrath in defeating Nidhogg. So the legend goes anyways.
But one can choose to take a patron deity for a reason as simple as it coinciding with their birthdate, similar to how we view the Western and Eastern Zodiacs.
A crafter may also choose to worship Byregot, the Builder. A thaumaturge, Nald'thal. A wealthy man, Nald specifically. A wandering minstrel may choose to walk the path of Oschon. Perhaps you choose to worship all twelve, or none at all. It varies person by person and for whatever reason truthfully.
There's no solid lore on why patron deities are chosen person by person though.