It is not that Somnath Mahadev has higher values then other Shiva lingas. Somnath Mahadev is the first Jyotirling among the 12 Jyotirlings. All the 12 jyotirlings have different importance and symbolism, you can't compare any of the Jyotirlings as its said Lord Shiva himself is present there and Lord Shiva is the same. Its just that Somnath Mahadev is taken first in shlok. To know more about Jyotirlings, refer this.
No it is nothing about order or nothing like higher value. SID M is absolutely right that it is taken first in shloka.
Importance of Somnath Jyotirlinga
Somanatha Jyotirlinga which is shiva's manifestation for protection of moon, when Chandra dev was cursed.
On the prayer of mother of "Asuras" demons -> Asurmata , Lord Shiva blessed her that if any of her sons , with pure heart, prays to Shiva with Somanatha Jyotirlinga , will be illegible for heaven directly!!
So Many demons entered in heaven and Indra did not like that. So he went to Vishnu who denied that he can not do anything against Shiva's will. Indra then went to mother of devas(deities) and asked her to pray to Parvati(Shakti).
Parvati promised her that she will help Indra and she sent Ganesha to stop Asuras from entering heaven. Then Lord Shiva and Parvati appeared and Shiva asked Ganesha to stop. Shiva told that Somnatha is just a way to heaven for those who are asura mata's sons. Meanwhile Rishi Kashyap asks his wife asuramata about the causes in heavan due to asuras. She asks mahadev to take his blessings back, but shiva says, any body who is wishing to go to heavan, if with pure heart prays to Somnatha Jyotirlinga, his wish will be fulfilled.
And thus it has the importance that Somnath Mahaev's prayer from pure heart may bring you heaven!!
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