There's quite a few things you could note from Ancient Sparta that portrays the significance of religious festivals and religion in Spartan society, I'll list a few pieces of evidence that demonstrates this significance.
- Strict adherence to religious ritual caused them to be mocked by other Greek Poleis. --> This is demonstrated by Herodotus when referring to the Battle of Marathon; "The Spartans, though moved by the appeal, and willing to send help to Athens were unable to send it promptly because they did not wish to break their law... they said they could not take the field until the moon was full." (This historical evidence indicates that religion may have been more important to the Spartans than displaying their military prowess.)
- Herodotus outlined a time in 480BC of the Battle of Thermopylae where only 300 soldiers under King Leonidas could be sent as a small composite force. --> This was because of the Karneia religious festival was still in procession and only when it was over could the spartans "march with all the troops at their disposal."
- From Thucydides: The gods were at the top of the chain of command that ran down through Spartan society. Their traditional rules, about festivals and sanctuary and the like, were there to be obeyed without question; and amid life's contingencies it was constantly necessary to seek further specific instructions through divination supervised by the humans just below them in the chain of command.
- "Fear of the Gods, deisidaimonia, was a particular form of that fear which in Greek thought was the foundation of social discipline." - Aechylus (In Hodkinson).
- "Those who honour the gods most finely with choruses are best in war" - Socrates (this demonstrates the significance of Spartan religious festivals).
For the Hyakinthia: Athenaus writes an account of the ritual; a three day festival, it includes a mourning for Hyakinthos and a general celebration of the God Apollo. J.T Hooker proposed the festival may have been a celebration for the dead, with an offered thanks for life as well. He links it to old Dorian festivals - in particular the Pythian games at Delphi. The festival itself included music played by young boys to the Gods, dancers, chariot races, sacrificed and large public feasts. This image is provided by in the play 'Lysistrata' by Aristophanes, an outpouring of joy, religious reverence, and enthusiastic dancing and movement.
Karneia:
The Karneia was celebrated in the holy month of Karneios (August / September) taking its name from the Ram god. Unearthed coins from this region depict this god (Apollo Karneios) as a horned God. Sacrificed ceremonies must have been undertaken as a line from 'Theoritus' suggests a shepherd was flattening a ram to be sacrificed to Apollo at the Karneia. The writer Sosibus suggests the origins of the festival lay in the founding of Sparta by the sons of Herakles. Rituals in the festival include the procession of model rafts, the symbols of the returning of Herakles sons. Races were held where a runner was wearing a garland of wool for the ram God and ran from other boys in the city. If he was caught, the omens of Sparta would be beneficial to the realm. Thucydides tells us the importance of this festival because Spartans withdrew in 481BC to participate in the Karneia. He also suggests the month of Karneois was sacred to the Dorians.
Gymnopaedia:
The very word relating to the festival comes from two Greek words meaning 'unarmed' and 'to dance'. At this 5 day annual event athletic contests were held by the young men. Boys sang of great deeds they were to undertake when grown, and fight tests of endurance in the hot summer - July sun. A wrestling dance 'Anopale' was performed as a fluid and graceful act, and a lively marching dance known as the 'Embaterion' was also adopted into the festival. Plato mentioned 'terrific endurance' at the festival 'as they flight against the baking'. It seems thus, a Festival of ordeal and endurance. Sosibus suggests that the Gymnoaediae may have been a commoration of champions who won the Battle against Argives in the 6th century BC, a level of which all Spartan youths may have aimed to achieve. This festivals was an exclusive one which banned unmarried men from participating in it, it is unclear at what age youth had to marry by. (Sparta boys participated so there must have been an age limit).
There's also a tonne of archaeological evidence for the practices of the festivals:
- Votive offerings - Coins, masks, pottery, miniature figurines.
- Sacrifices - Eg (piglet for the two kings), Herodotus, Archaeological sites - such as Altars.
- Prayers and Hymns - Written evidence, Alcman and Tyrtaeus.
- Libations - again written evidence and archaeological sites - Altars.
- Divination and Oracles - Kings mainly concerned with - Delphic Oracle, Lycurgus, Great Rhetra.