Jaya Nitai! Others have given wonderful answers. I would like to actually quote an article written by our Acharya Srila Bhaktivinoda Thakur on the reason why there are many different religions and sects:
Sectarianism is a natural byproduct of the Absolute Truth. When acaryas first ascertain and instruct the Truth, it is not polluted with sectarianism. But the rules and regulations received through disciplic succession regarding the goal and the method of achieving it are changed in due course of time according to the mentality and locale of the people. A rule that is followed by one society is not necessarily accepted in another society. That is why one community is different from another. As a community gradually develops more respect for its own standards, it develops hatred towards other communities and considers their standards inferior. These sectarian symptoms are seen in all countries since time immemorial. This is prominent amongst neophytes and found to some extent amongst madhyama-adhikaris. Amongst uttama-adhikaris, however, there is no trace of sectarianism. Adherence to a particular standart is the prominent symptom of a society. There are three types of standards-alocakagata, alocanagata, and alocyagata. Alocakagata is when sectarianists accept some external signs. Examples of alocakagata are tilaka, neck beads, saffron robes, and the baptism that is practiced abroad.
The different activities practiced in the process of worship are called alocanagata. Examples of alocanagata are sacrifices, austerities, fire sacrifices, vows, studying scriptures, deity worship, constructing temples, respecting the purity of various trees and rivers, dressing like sannyasis, acting like acaryas, dressing like brahmacaris or grhasthas, closing one s eyes, respecting particular types of books, rules and regulations in eating, and respecting the purity of particular times and places. The examples of alocyagata are attributing personalism or impersonalism on the Supreme Lord, installing deities, exhibiting the mood of an incarnation of the Lord, speculating on heaven and hell, and describing the future destination of the soul. The different forms of these spiritual activities create divisions of sectarianism.
Differences that arise from places, times, languages, behaviors, foods, dresses, and natures of various communities are incorporated within people s spiritual practices and gradually make one community so completely different from another community that even the consideration that everyone is a human being may cease to exist. Due to these differences there is disagreement, cessation of social intercourse, and fighting, even up to the point of killing one another. When an asslike mentality becomes prominent within the kanistha-adhikaris, they certainly indulge in these things. But if they develop a swanlike mentality, then they do not take part in quarrels; rather, they endeavor to attain a higher level. Madhyama-adhikaris do not quarrel so much about external standards, but they are always attacked by philosophical disagreements. Sometimes they condemn the standards of neophytes and establish their own standards as superior. They condemn the neophytes deity worship in order to establish the worshipable Lord as formless. In such cases, they are also considered asslike people. Otherwise, if they had a swanlike mentality and a desire to attain a higher level, they would respect others practices and inquire about higher topics.
Contradictions actually arise only due to asslike mentality. Swanlike persons consider the necessity for different practices according to one‘s qualification, so they are naturally detached from sectarian quarrels. In this regard, it should be understood that both asslike and swanlike people are found amongst the kanistha-adhikaris and madhyama-adhikaris. I do not expect that asslike people will accept this book with respect. If neophytes and madhyama-adhikaris become completely indifferent in regard to the contradictions found in various practices and try to advance further, then they become swanlike persons. Then they are our respectable and dear friends. Although swanlike personalities may accept a particular practice from birth or childhood according to instructions they have received, they nevertheless remain indifferent and nonsectarian