Śrīmat-tripura-sundarī श्रीमत्-त्रिपुर-सुन्दरी (997)

Śiva is known as Tripura. Tri means three and pura means fortress, castle etc. And Tripura means three fortresses. Three fortresses refer to the three unique acts of Śiva, the creation, sustenance and dissolution. Each of these acts is supervised by Brahma, Viṣṇu and Rudra.  Since Śiva is the overall controller of all these acts, He is known as Tripura-Sundarā (Sundara is a suffix indicating his handsome appearance). It is said that Brahma, Viṣṇu and Rudra are the parts of Śiva’s body. His consort is known as Tripura Sundarī (Sundarī is the feminine gender of Sundara). This has been explained in nāma 787 Tripureśī.

In Vāmakeśvarīmatam (IV.4), Śiva addresses Bhairavi “Dear One! Tripura is the ultimate primordial Śaktī, the light of manifestation. She, as Mātṛkā, through Her gross and subtle aspects give birth to the three worlds. At dissolution, She is the abode of all things (meaning the tattva-s or principles), still remaining Herself (nāma 571). After She emanates, there is no need for the Lord (Śiva). Devoid of Śaktī, He cannot act.”

Tripura also means Vāmā, Śikhā and Jyeṣṭā, the three deities presiding over the three lines of the innermost triangle of Śrī Cakra looking after creation, sustenance and dissolution. Each of the lines of this triangle is known as pura or a fort. Since She is the ultimate unified Śaktī controlling the three pura-s, She is known as Tripura
She as the Brahman causes the process of manifestation through the three kūṭa-s of Pañcadaśī mantra referring respectively to icchā śaktī, jñāna śaktī and kriyā śaktī. Hence, She is known as Mahā Tripura Sundari (mahā means supreme).
{Further reading: She is Ādi Śaktī from whom all the triads (tripura) are derived. Ādi Śaktī is the sum total of all the energy forms, the cause of material creation. Time to time, this divine energy manifests itself in various forms and shapes that we are able to construe. The entire universe is filled either with matter or with energy. In other words, what we call as void is filled with gravitational force or electromagnetic fields. It has been proved scientifically, that the universe was much smaller that it appears today and will expand further leading to the ultimate collapse known as annihilation. The expansion of the universe stops at some point of time and the universe begins its contraction. When the contraction is complete, the universe reaches its original state of Big Bang. Śaktī as the kinetic energy and as the Supreme administrator causes the conception, expansion and contraction (the three primary acts of Śaktī, each in the form of a pura; hence She is known as Tripura Sundarī). The kinetic energy is derived from the static energy or the original source of the Big Bang known as Śiva.}

Śrī Śivā श्री शिवा (998)

The Supreme energy of Śiva personified as His wife. Śiva also means liberation. She has been addressed as Śiva in nāma 53. In this nāma Vāc Devi-s have prefixed Śrī to Śivā as they wanted to declare Her most auspicious form to the world. Śrī is the Lakṣmī bīja and the form of Lakṣmī is considered as one of the most auspicious forms. The one who is able to visualise Her as Śrī Śivā is drenched in bliss as he is going to have a view of Śiva-Śaktī (Śiva-Śaktī sāmarasya) combine in the next nāma and to ultimately merge with Her in the last nāma of this Sahasranāma. Realisation can take place only in the advanced stage of bliss.
The final phase of the worshipper is being portrayed through this nāma. The merger of the feminine energy known as kuṇḍalinī before its final union (the next nāma) with the masculine principle known as Śiva, indicating the culmination of spiritual practice. 
Śiva means the purity of the highest order. Māṇḍūkya Upaniṣad (7) says, “prapañcopaśamam śāntam śivam” which means the total cessation of the world as such, the sum total of that is good, one without a second is the Brahman (it means to say that śivam is all that is good). 
Yajur Veda (IV.v.10) says, yā te rudra śivā tanuḥ śivā viśvāhabheṣajī (Śrī Rudraṁ 10.3) which means ‘that auspicious form of yours, Oh Rudra! Which is auspicious and ever healing.’ Mahānārāyaṇa Upaniṣad (21) also says “May the Supreme, who is the ruler of all knowledge, controller of all created beings, the preserver of the Vedas and the one overlord of Hiraṇyagarbha, be gracious (Śivaḥ) to me.”
Vāc Devi-s should have chosen to place this nāma at the end as they would have liked to articulate the enlightened and transformed vision of the mystic for whom Her paradoxical omnipresence has become a perceivable experience. This nāma is the prologue to the next nāma, the most significant one as it discourses the macrocosmic conceptualisation.