sorry for the double post, I missed riot4j's reply
riot4j said:
...Why would He say it if He is not really the only one. Or why would someone lie for Him...The problem may come if some other God claimed that he too is the only one true God, because then there wil be like "many truths"
What I meant by the problem here, is even with your reiteration, you still are saying that since it was said it, it must be true. That is called blind faith. If you have faith that's fine, I don't want to attack that. It's the part of accepting it just because it's true.
The reason that is generally bad is the answer to the first part of your question...people lie. The do it for all kinds of reasons, like money, power, or fun. But people lie. So it's okay to believe, but I would hope you have more reasons than just because he said so.
Also like other people pointed out why would he have to say he was the true god in the first place? And for any monotheistic religion, by definition, they only have one god, and it is viewed as the true god. So even though they don't say it outright, they are viewed/believed as the one true god.
riot4j said:
Who is Vishnu? Would you say more about him?
Vishnu is a god of Hinduism. Not a bad religion. But since you asked, I looked it up, and that is another poly religion. The other main gods are Brahma and Shiva. Just do a google search on Vishnu or Hinduism.
riot4j said:
The thing is if there is only one God who is the true god why worship so many other gods who are not true?(given there is one true God)
What you are asking is if you believe that God is the one true God, why believe other Gods...when we assume like you ask that there is one true God...then you don't believe in others.
However if we don't assume that belief in the one true God, then you believe another God is the true God (excluding polytheism) and then you have to find another way to find out who is right.