In plain words
Śaiva worship: 'Liṅgaṃ sarvakālam' [the liṅga is eternal] — the liṅga is the root cause of the state and movement of the [elemental] principles beginning with earth. That itself is the very form of Parama Śiva. Attaining the personal iṣṭa-liṅga alone is liberation — so it is said.