मग्नः स्वचित्तेन प्रविशेत्
In plain words
Immersed, he should enter with his own .
The commentators
Śivasūtra with Kṣemarāja's Vimarśinī
अत्रोपायमाह- मग्नः स्वचित्तेन प्रविशेत् ॥ २१ ॥ प्राणादिस्थूलभावं तु त्यक्त्वा सूक्ष्ममथान्तरम् । सूक्ष्मातीतं तु परमं स्पन्दनं लभ्यते यतः ॥ इत्युपक्रम्य … प्रविशेत्तत्स्वचेतसा ॥ इति-श्रीमृत्युजिद्भट्टारकनिरूपितनीत्या प्राणायाम-ध्यान-धारणादिस्थूलोपायान् परित्यज्य स्वचित्तेन अविकल्पकरूपेण अन्तर्मुखान्तरविमर्शचमत्कारात्मना संवेदनेन प्रविशेत् समाविशेत् । कीदृक् सन् ? मग्नः शरीरप्राणादिप्रमातृतां तत्रैव चिच्चमत्काररसे मज्जनेन प्रशमयन् । तदुक्तं श्रीस्वच्छन्दे व्यापारं मानसं त्यक्त्वा बोधरूपेण योजयेत् । तदा शिवत्वमभ्येति पशुर्मुक्तो भवार्णवात् ॥ इति । श्रीविज्ञानभट्टारकेऽपि मानसं चेतना शक्तिरात्मा चेति चतुष्टयम् । यदा प्रिये परिक्षीणं तदा तद्भैरवं वपुः ॥ इति । एतदेव ज्ञानगर्भे स्तोत्रे विहाय सकलाः क्रिया जननि मानसीः सर्वतो विमुक्तकरणक्रियानुसृतिपारतन्त्र्योज्ज्वलम् । स्थितैस्त्वदनुभावतः सपदि वेद्यते सा परा दशा नृभिरतन्द्रितासमसुखामृतस्यन्दिनी ॥ इत्यनेन महागुरुभिर्निबद्धम् ॥ २१ ॥
In plain words
Immersed, let him enter with his own mind. He states the means for this: By the way set out in the Mṛtyujit Bhaṭṭāraka, beginning: "Leaving the gross state of prāṇa and the rest, and then the subtle, the inner, that by which the supreme spanda beyond the subtle is gained …" and going on: "… let him enter that with his own mind," let him leave aside the gross means, prāṇāyāma, meditation, dhāraṇā and the rest, and enter, that is, be absorbed, with his own mind: with an awareness free of thought-constructs, whose nature is the wonder of inner reflective awareness turned within. Being what? Immersed: stilling the sense of being the knower as body, prāṇa and the rest, by plunging it in that very savour of the wonder of consciousness. As the Svacchanda says: "Leaving the activity of the mind, let him join it to the form of awakening; then the paśu attains Śivahood, freed from the ocean of becoming." And the Vijñānabhaṭṭāraka too: "Mind, intellect, power and self: when this fourfold set, beloved, has wasted away, then that is the form of Bhairava." The great teacher has set down this very point in the hymn Jñānagarbha: "Leaving every activity of the mind, O Mother, men who abide so, through your power, at once come to know that supreme state, bright with freedom from depending on the activity of the instruments on every side, which streams with the nectar of a bliss unwearied and without equal."