All religions cannot be true.
One is right and the other is wrong.
There is an objective truth.
While most religions have some kind of similiar moral code because God has implanted right and wrong on our consciences, they disagree on virtually every major issue, including the nature of God, the nature of man, sin, salvation, heaven, hell, and creation.
How can you believe in two religions at the same time?
If you do, then you are implying that there is no objective truth.
Jews, Christians, and Muslims believe in different versions of a theistic God, while most Hindus and New Agers believe that everything that exists is part of an impersonal, pantheistic force they call God.
Many Hindus believe that evil is a complete illusion, while Christians, Muslims, and Jews believe that evil is real.
Christians believe that people are saved by grace while all other religions, if they believe in salvation at all, teach some kind of salvation by good works (the definition of "good" and what one is saved from varies greatly).
All religions do not believe the same things.
Believe it or not, atheism is a belief.