उमामहेश्वरव्रतं—पञ्चाक्षरमन्त्रस्य माहात्म्यं, न्यासः, जपविधिः, सदाचारः, विनियोगः
पेर्फ़ोर्मिन्ग् आसन अनासनः शयानो वा रथ्यायां शूद्रसन्निधौ रक्तभूम्यां च खट्वायां न जपेज्जापकस् तथा
performing āsana anāsanaḥ śayāno vā rathyāyāṃ śūdrasannidhau raktabhūmyāṃ ca khaṭvāyāṃ na japejjāpakas tathā
Likewise, the practitioner of japa should not recite while shifting about without a steady seat, nor while lying down; nor in a public street, nor in the close presence of a Śūdra, nor upon blood-stained ground, nor upon a bed. Such conditions obstruct the purity and inward one-pointedness required for approaching Pati (Śiva) through mantra.
Suta Goswami
It sets boundary-conditions for japa so the worshipper maintains śauca (ritual purity) and ekāgratā (one-pointedness), allowing mantra to become an effective means of approaching the Linga as Pati.
Shiva is implied as Pati—approached through mantra only when the pashu (individual soul) restrains distracting and impure conditions that strengthen pāśa (bondage) like restlessness and tamasic surroundings.
Mantra-japa discipline: recite in a stable, clean, and inwardly conducive setting—avoiding lying down, public roads, impure places, and other proximity rules—so the mantra remains sāttvika and focused.