Among all the human tendencies, tendency to unify the things is one of the most dominant. People though respect diversity, are striving within to unify the things. The religions also were not able to escape from these unificationists. Though this effort of unify can simply the things, unification of religions is not at all desirable. For the ages, may philosophers, mystics and even emperors have worked on this concept of unification and they had very positive and constructive views behind those efforts. But, instead of so many efforts, this unification is not possible. It is good that unification is not possible, because this very concept of unification of religions is irreligious.
                           
Unification was tried in two ways. The one was to actually unify the religions and start a new religion which had all the good thoughts collected from all the religions. This effort was done by Emperor Akbar and then by a saint named Basaweshwar. Another effort consists of just pointing out similarities between religions and to follow them with equal devotion. Mahatma Gandhi and some theosophical thinkers worked a lot on this concept.

I think it is needed to be understood why such efforts are not desirable. It is said that religion is not something which is to be taken from others. It is something which you should generate within yourself. Each person should have his different religion. Many people point out similarities between Geeta and Holy Quran. But, it is something like deliberately putting apples with mangoes. Each person is unique. Krishna was different and Prophet Mohammad was different. Each one had his own unique way. It is a sad situation that people need to follow someone; a Krishna or a Buddha. Actually, each person has right to be a Buddha. Every person does not have this situation favorable so that he can blossom into an enlightened one. So, he starts following someone who has blossomed. From here, the term religion comes into existence. It is like someone has found the way and he is sharing it with others. Someone has learned an instrument then he shares his journey. But the point which is to be noted is that, while doing so, individuality of the learner is not damaged.
                            
Unification asks you to be identical. It does not care for the individuality. The masters, though they influenced highly the lives of their disciples, never compromised with their individuality. Buddha has rightly said -

“If you find me standing on your way, just kill me and go ahead.”
               
It simply means that, Buddha did not want individuality of his disciples to be affected by him. But when master is dead, only the rules remain. Only theories remain. Which are just followed blindly and which simply kills the individuality. In world there are dozens of religions, which at least allow a little bit of diversity. This diversity is too little but it is better than having a single religion.
                 
Spiritual progress is not a mass phenomenon. Information can be given to masses. Information has nothing to do with the individuality of person, so it is fine if we provide some information to thousand people sitting at one place. But, religion or spirituality deals with the individuality of persons. Each and every person is going to be a different. The Zen master used to work on each disciple separately. Famous Russian mystic, George Gurdjieff worked differently on each of his disciples. The only reason is, every person needs a different religion as per his individuality. Only some particular crop can grow in a specific soil. Same way, only a specific spiritual way is suitable for specific type of persons. When we are talking about religion, it simply applies same rules to all of its followers without considering their individuality. It is good that at least we are having a dozen of religions. We have some choice to choose what suits us the best. If this much of choice is also taken away, the situation will be even more pathetic.
                                
So, instead of unification of religions, what we need is splitting of religions, based on more and more fine and subtle qualities of individuals. Each person should have the right to select the religion which consists of techniques which will work best on his psychological parameters. The most important thing is the religion which will lead its follower to such a position that he does not need to follow the religion, is the true religion. Unification of religions is the most irreligious thing that can ever happen