Sri Vishishtadvaita is the main principle of Sri-Vaisnav Sampradaye.and it is very beautiful described and easily can understand by anyone.
There are total three famous opinions in Vaisnav Samprdaye:
1. Advaita - Sri Sankracharya
2. Dvaita - Sri Madvacharaya
3. Vishishtadvaita - Sri Ramanujacharya
There are total three types of Shrutis in Vedas/Scriptures:
1. Abhed Shruti ( Advaita)- Where Supreme lord (Super-Soul) and living-entity (Sub-Soul) is one they are not different from each other.
2. Bhed Shruti (Dvaita)- Where Supreme Lord (Super-Soul) and living-entity (individual soul) is not one but they are different from each other.
3. Gatak Shruti ( Vishishtadvaita)- It is Solution of above two opposite Elements (Abhed tatva & Bhed tatva) is truth .
Sri Vishishtavaidta is based on Gatak Shruti.and this thing is also beautifully described in the Sri-Bhasya by the author of Sri-Bhasya, Sri-Ramanujacharya.
Every Mysterious Elements ,principle & ArthaPanchak** are depend on Vishishtavaita Prinicple.
If you will understand this main principle then you can easily understand all mysterious thing which is in Sri-Vaishnav Sampradaye.This Principal gives solution of Gatak Shruti even also gives a solution of the Abhed(Advaita) and Bhed(Dvaita).
Generally people think that this principle is only applicable for those who belongs to Sri-Vaisnav (Ramanuja) Sampradya.But it's wrong, because this principle is already presented before it was invented. Sri- Ramanuja only put light on this principle through the help of Scirputers (Granths/Purans).
As we know Shreemad-Bhagvad Gita is universally accepted.Elements which were described by Sri Lord Krishna to Arjun is all are Sri Vishitadvaita principle.
Let's we will understand Sri-Vishistadvaita Principle from Shreemad-Bhagvad Gita.
क्षेत्रज्ञं चापि मां विद्धि सर्वक्षेत्रेषु भारत।
क्षेत्रक्षेत्रज्ञयोर्ज्ञानं यत्तज्ज्ञानं मतं मम।।13.3।।
-And know Me also as the Kṣetrajña in all Fields, O Arjuna. The knowledge of both the Field
and its Knower is, in My view, the highest knowledge.
Even Sri-Ramanuja is also commented in Sri-Bhasya:" The Characteristics & Form of nature and soul are to live as body of Supreme Lord.
अहमात्मा गुडाकेश सर्वभूताशयस्थितः।
अहमादिश्च मध्यं च भूतानामन्त एव च।।10.20।।
-I am the Self, O Gudakesha (Arjuna —Conqueror-of-sleep), dwelling in the hearts of all beings.
I verily am the beginning, the middle and also the end of all beings.
Understand by Visishadivata: In the body there is one soul and also there is one super-soul who is also present within the body. ( Four-armed Visnu).So, That's mean Supreme Lord, living-entity(we) and nature is not one.It's rebuttal or disclose the principle of Advaita.And also it can't be distinct or apart like the body and soul can't be apart from each other.So, It's rebuttal or disclose the principle of Dvaita.
उत्तमः पुरुषस्त्वन्यः परमात्मेत्युदाहृतः।
यो लोकत्रयमाविश्य बिभर्त्यव्यय ईश्वरः।।15.17।।
-Distinct from these is the Supreme Person, described as the Supreme Self [in the Vedas], He
who pervading the threefold universe, supports it as the Immutable One and the Lord.
By Visishtadivata : Here it's rebuttal the Abhed Shruti ( Advaita). The Greatest man Supreme lord who is distinct from us.Even though he is enter in us and take care of us and also maintain our body system. So, we can directly understand from the Sloka Supreme Lord is different from us.
अहं वैश्वानरो भूत्वा प्राणिनां देहमाश्रितः।
प्राणापानसमायुक्तः पचाम्यन्नं चतुर्विधम्।।15.14।।
-Becoming the Vaishvanara Agni, I function within the bodies of all living beings. In
association with the Prana and the Apana, I digest the four kinds of food.
By Visishtadivata : Lord Visnu is so Mercy-full that he enters in us as supersoul and digest the food which is taken by us.If lord is not distinct from us then how he can digest our Food?.So,It's rebuttal or disclose the principle of Advaita.
If lord is distinct from us then we don't need to think of digest the food. It's means we are capable to digest food by oursleves. It's also not right.So,It's rebuttal or disclose the principle of Dvaita.
The Visishtadvaita principle is tell us like as we can't discriminate the white color from the white clothes. even though they both are different from each other like same as Davita and Advaita can't be discriminate from each other. even thogh they both are different from each other and same as we and Suprme Lord Visnu are different from each other but also not differentiate from each other.
There are so many slokas in Bhagvad Gita where we can see the principle of Visisthadvaita like 18.61,15.15,10.31,10.42,15.13,7.6 to 7.12, 9.4 to 9.6 and 10.41.
Sri-Ramanuja the great saint we thankful to him because he disclose the confusion of Dvaita and Advaita.
Jay Shree Krishna.
Om Namo Narayan.