When Morgoth destroys the trees, the angelic powers, the Valar, are left without light. Fëanor's Silmarils, though, may hold the key, as they contain the holy light. Possessive of his sub-creation, Fëanor leaves the Blessed Realm, taking with him the Silmarils, containing a light beyond his ability to create.
Fëanor did not take the Silmarils with him to Middle Earth. He went to get then back, since they had been stolen by Morgoth. However, when he learned of the their theft he had already refused to allow one of the Silmarils to be used to revive the dying trees.
If I remember correctly.