Lord Ardhanārishwarā, epitome of oneness of Lord Shiva and Parvati represents the source of the world
Soundarya Lahari Sloka 1
Śivaḥ śaktyā yukto yadi bhavati śaktaḥ prabhavituṁ
na cedevaṁ devo na khalu kuśalaḥ spanditumapi|
praṇantuṁ stothuṁ vā kathamakṛtapuṇyaḥ prabhavati||
शिवः शक्त्या युक्तो यदि भवति शक्तः प्रभवितुं
न चेदेवं देवो न खलु कुशलः स्पन्दितुमपि।
प्रणन्तुं स्तोतुं वा कथमकृतपुण्यः प्रभवति॥
Lord Shiva is able to do creation in this world only along with Shakthi.
Without her, even an inch he cannot move, and so how can one who does not do good deeds or one who does not sing your praise become adequate to worship you, OH, goddess of mine, who is worshipped by the trinity.
Because of her functional nature, Divine Mother becomes supremely important.
This adores the Supreme Mother, who is ever compassionate, carrying out all the activities to sustain the universe. Those who have good karmas acquired over past births alone become capable of seeking her through various forms of her worship.
When it is not easy for Brahmā, Viṣṇu and Purānic Śiva to worship her, the kind of good karmas one needs to worship her through Śrīvidyā Upāsana is subtly explained in this verse.