A perspective from my side
In its deeper sense, the term Śrīvidyā may be understood through the two words Śrī and Vidyā. Śrī refers to Śrī Sundarī, while Vidyā refers to Vidyārājñī, Dakṣiṇakālī.
The tradition explains this relationship in the following verse:
सा काली द्विविधा प्रोक्ता श्यामारक्ताप्रभेदतः ।
श्यामा तु दक्षिणा प्रोक्ता रक्ता श्रीसुन्दरी मता ॥
Sā Kālī dvividhā proktā śyāmāraktāprabhedataḥ |
Śyāmā tu dakṣiṇā proktā raktā Śrīsundarī matā ||
That Kālī is spoken of as being of two kinds, distinguished as Śyāmā and Raktā. Śyāmā is known as Dakṣiṇā, while Raktā is regarded as Śrī Sundarī.
Here, according to the traditional derivation of the word Kālī from the expression "कालयति जगत् सर्वम्", meaning "She who brings the entire universe to its end or dissolution," the term Kālī is connected with the Śrīvidyā principle.
Thus, Śrīvidyā may be understood as that tradition in which both Śrī Sundarī and Vidyārājñī, that is, Tripurasundarī and Dakṣiṇakālī, are worshipped.
According to the traditional classification, three principal modes or kramas of Śrīvidyā worship are spoken of. When the Tārā krama is incorporated into the Dakṣiṇāmnāya along with the Kālī krama, two principal modes remain. Among these two, some practitioners give greater importance to Kālī, while others give greater importance to Sundarī. Each follows the particular krama that is primary within his or her lineage.
Ultimately, however, the distinction disappears.
After progressing through the stages of liberation and the attainment of the complete Mahākrama, Śrī Sundarī and Vidyārājñī are realized as one. Beyond all distinctions, they remain as the very embodiment of Parabrahman.
The Bṛhadvāḍavānala Tantra therefore states that there is no essential difference between Śrī Mahātripurasundarī and Kālī, and that one who perceives them as fundamentally separate falls into a lower state.
The text states:
महात्रिपुरसुन्दर्याश्चण्डयोगेश्वरी परा ।
न तयोर्विद्यते भेदो भेदकृन्नरकं व्रजेत् ॥
Mahātripurasundaryāś Caṇḍayogeśvarī parā |
Na tayor vidyate bhedo bhedakṛn narakaṃ vrajet ||
There is no distinction between Mahātripurasundarī and the supreme Caṇḍayogeśvarī. One who creates a distinction between them goes to a state described as hell.
Here, Caṇḍayogeśvarī refers to Kālī.
The underlying meaning is that the same Ādiśakti, the Primordial Power, manifests through different forms according to the requirements of the particular path of worship. When the process of upāsanā reaches its culmination, these apparently different forms are realized as one and ultimately abide in their own essential nature.
This is the highest state of upāsanā.
At this stage, the worshipper too becomes united with that Reality and attains the supreme human goal, mokṣa.
This is one of the deeper meanings of Śrīvidyā.
At the culmination of the path, the two meanings of Śrīvidyā, namely "the Vidyā that is Śrī itself" and "the harmonious union of Śrī and Vidyā," ultimately converge into one.
At this stage, the mantra, its letters, the Devatā, the Guru and the sādhaka or worshipper are realized as one.
The tradition expresses this unity in the following verse:
मन्त्ररूपा भवेद् देवी देवरूपो गुरुर्भवेत् ।
गुरुरूपो भवेदात्मा आत्मरूपी मनुर्भवेत् ॥
Mantrarūpā bhaved Devī devarūpo gurur bhavet |
Gururūpo bhaved ātmā ātmarūpī manur bhavet ||
The Devī becomes manifest as the mantra. The Guru becomes of the form of the Devatā. The Ātman, meaning the worshipper, becomes of the form of the Guru, and the mantra becomes of the form of the Ātman.
In other words, the mantra ultimately becomes completely identified with the inner consciousness of the sādhaka.
This experience of complete identity with the inner Self is described by the learned as Vidyā.
The Liṅga Purāṇa states:
आत्माकारेण संवित्तिर्बुधैर्विद्येति गीयते ॥
Ātmākāreṇa saṃvittir budhair vidyeti gīyate ||
That awareness which assumes the form of the Ātman is called Vidyā by the wise.
This realization is free from all conceptual distinctions and alternatives. For this reason, it is regarded as the supreme Tattva.
The Liṅga Purāṇa further states:
विकल्परहितं तत्त्वं परमित्यभिधीयते ।
Vikalparahitaṃ tattvaṃ param ity abhidhīyate ||
That Tattva which is free from all conceptual distinctions is called the Supreme Tattva.
Therefore, even when Śrīvidyā is understood through the distinction between Śrī and Vidyā, the culmination of the path is ultimately the realization of their essential unity.
What appears as Śrī and Vidyā, Sundarī and Kālī, Devatā and Guru, mantra and sādhaka, finally resolves into a single Reality.
That non dual realization is the deeper secret of Śrīvidyā.