Hinduism as we know today is the product of syncretic combination of various Philosophical and religious thoughts of the day. The major formative force was indeed Christianity.

When the Harappa civilization was unearthed, linguists from all over the world were hard at work to decipher the scripts. I have met some of them back in 1950 while in school. The baffling thing was those writing were far removed from “Indo-European” scripts. All attempts to decipher in terms of Indo-European languages failed while it yielded fair results even in those days using Kodum Tamil as base. Evidently there existed a language system which was far more ancient than Sanskrit.

The Grantha writing system was developed in the 5th c. AD and was the protolanguage of the modern Tamil and was used to write Sanskrit. Inscriptions in Early Grantha, dating from the 5th to 6th c. AD on copper plates and stone monuments were found dating from the Period of the Pal lavas near Chennai (Madras). Originally Grantha was used for writing Sanskrit. Nagiri came into use only after the 7th c. AD.

Nirad Chaudhuri points out that 'the Hindu religious texts with the exception of the Vedas and their ancillary treatises, are all in classical Sanskrit. He says that in their present form none would be earlier than the fourth century A.D'. Though it is often argued that these epic and philosophical works were in existence long before they were written down and were handed down through generations by oral transmission, it is quite unlikely because at some point the translation occurred from Vedic to Grantha or to Sanskrit. Hence its original form or content cannot be guaranteed. It is quite likely that the form and content changed during this period as it does even today (in spite of the writing)

'The Gita is written in good classical Sanskrit, and epigraphic evidence clearly shows that the Gita could not have been written before the second century A.D.’ It is probably of much later period.

'The earliest epigraphic evidence on languages employed in India comes from the inscriptions of Asoka inscribed in third century B.C. Asoka took care that his messages were intelligible to all and he used a particular kind of Prakrit. He even translated his messages to Greek and Aramaic. But, there are no inscriptions in Sanskrit. The first evidence of Sanskrit is seen around A.D.150 and from the fifth century A.D. and classical Sanskrit is seen to be the dominant language in these inscriptions.'

It is evident therefore that the early Vedic religion underwent a drastic change during the period following the 2nd c, which culminated, into the various vedantic teachings, which we know today as Hinduism.

The major political influence of the period soon before the period was the invasions of Greek. Alexander the great

The invasion did succeed to a certain extent. Seleucidan kingdom was established in part of India that was conquered. Subsequently, several Greek kingdoms came into existence in the Punjab/Multan/Afghan regions. One of the most famous Greek kings was Menander. Menander was scholar in Buddhism. Greek and Indian art fused and gave rise to a new art form called Gandara. It was the Greeks (philosophical form by Plato and the Pythagoreans) who first introduced the idea of reincarnation to India. It does not appear in the earliest Hindu scriptures (the Rig Veda) but was developed at a later period in the Upanishads under the Greek influence.

Among the Indo-Parthian Empire was the Kingdom of Gondophorus in Taxila, which played an important part in shaping the religious history of India. It was Gondophorus who summoned St.Thomas into India who arrived in the Malabar Coast in AD 52. St. Thomas’ route of evangelization can be traced from the Acts of Thomas written around AD 300. Here is the approximate route.
 

  

The culmination of Upanishadic teachings actually came in by the 7^th to 10^th C AD when these were really crystallized.

Though each of the schools of Vedanta claim heritage from Godhead himself and claims its parampara through rshi tradition to manava parampara, the real exposition are found only in the Acharyas who lived in the  period later than 7^th c AD.   Here are the founders of the Theistic schools of Vedanta and their approximate times:

Sankara  788 –820 Advaita – Monism (Born in Kaladi, Kerala)

Ramanuja 1017-1137 Visistadvaita the Modified Non-dualist school. (Ramanuja (also known as Ilaya Perumal) was born to Kesava Perumal Somayaji Dikhsitar and Kanthimathi Ammal at Sriperum pudur. He was born in Kaliyuga year 4119 which corresponds to1017 AD)

Madhva (Ananda Tirtha) 1197-1273 Dvaita the Dualist school.

Nimbarka late C13? (Nimbarka was born of Aruna Muni and Jayanti Devi on the banks of  Godavari river) Dvaitadvaita the Dualist-non-dualist school.

Vallabha 1478-1530 Shudda Advaita- the Pure Advaita school.

Caitanya 1485-1533  followed by  Baladeva  early 18thc:  AcintyaBhedabheda - Incomprehensible Distinction-Non-distinctionism.

 Here is the Geographical settings of these teachers.

 

 

It will probably come as a surprise that the two maps overlaps exactly on each other. 

The only plausible explanation is that Vedic religion was transformed into Hinduism as we have come to know of by the reaction to two other religio-philosophical systems – Greek and Christian.  We have very little history of the growth and decay of these religious thoughts in documentation.  However we know that there was a powerful Christian presence in the Cauvery Area apart from the Christian Church  in Malankara (Malabar). As the Christian faith became powerful, there had been local reaction from the religions that were present.  Natural course of events produced  various syncretic form along with direct persecution.   We  know that there ensued a persecution to these Christian communities in the Andhra  and Tamil areas, that they were forced to migrate to Quilon and Thiruvanthapuram in Kerala.  We also know that they were perused by the then leaders of Hinduism.  Christian documentation indicate that a certain sorcerer Manicavachagar  actually came down to Quilon and reconverted 70 families back to Hindu fold.  Who actually is this Manicavacagar cannot be posotively identified.  It is normally assumed that this was the famous Gnostic Persian Prince Manicaen.  It could very well have been a Hindu Theosophist of the period.  It would be worthwhile to remember that a Gnostic controversy was at its climax in the Eastern Churches at that time.  Gnostic and Greek influence syncretised with the Christian doctrines actually produced the present day Hinduism. We can see exactly the same history repeated in the reconversion of tribal Christians. 

 

 An impassionate analysis will reveal the underlying syncretic layers. 

Thus Apium Forum remarks  ”When we study the development of religion and worship in India, before and after Christ, we can see that Christ and Christianity totally transformed religion and worship in India from the first century AD. Saivism first developed as a monotheistic doctrine and Siva was first called Isa which is the name for Jesus in the North. The avatar concept (God coming into the world in the form of a man) in Vaishnavism is the influence of Christianity.

Hindus in India consider Christianity as a foreign religion. However they do not realize how much early Indian Christianity has developed and molded their own religion, and, the revealed truths in their own faith point to Jesus Christ. I pray that we the Christians in India would take time to understand where the heart of every Hindu is, and, help guide them to The Truth in Christ Jesus by gently removing the barriers and obstacles without

Dr. D Devakala and  Dr. Alexander Harris has shown this development in the following time line.  On this can be added the St.Thomas history when the picture will be more clear.  This is shown below:

 

 

 

 

 

 

 

 

http://www.geocities.com\Athens\Parthenon\2104\index.html

 

Evidently the Hinduism as we know of today was the product of various religious and philosophical thoughts of the late Christian Era.  Among these were the Bhakthi marga and the centrality of the Ultimate Incarnation in the person of Isa  (Yesu) as preached by the Christians.  In the process, Christians were persecuted and forcefully converted and most churches in the interior syncretized and became part of Sivite and Vaishnavite traditions.  But Malankara Church survived the onslaught essentially because of their contact with the rest of the Christian world particularly of the Eastern churches of Persia.  Most of all Malankara had the help of the Syrian translation of the Bible, which was earnestly taught, in the Churches.  So Malankara churches survived the Gnostic and syncretic forces to this day.