"Let not your heart be troubled; ye believe in God, believe ALSO in me."
I am sure that at any given point during your day you hear people say they believe in God or that they believe there is a God or know God or think there is "something" out there; which may well be fine and dandy...but it is not enough!
What did Jesus just say in John 14:1? "...ye believe in God, believe ALSO in me."
You can believe in God all day long, but it is NOT enough! God sent Jesus into the world for a reason, not just for the heck of it. Muslims believe in God, although NOT the God of the Bible and they deny Jesus is the Son of God and God Almighty! God haters deny him, but they blame him when bad things happen. Either you believe God exists or you don't!
God is revealed in Jesus Christ; he "is the image of the invisible God." (Colossians 1:15)
Check out this verse from James 2:19, "Thou believest that there is ONE God; thou doest well: the devils ALSO believe, and tremble." This is a great verse. It is confirming that there is one God and that the people he is writing to believe this; and that devils also believe in God and tremble, even tremble with fear.
The mistake Muslims make is saying that Christians worship three Gods: the Father, the Son and Holy Spirit. To them, the simplicity of the Godhead is foolishness. And they don't care to know the truth, because the truth shall make them free. (John 8:32)
Time and time again, Jesus tried to convey the message that man needed only to believe in him for salvation. But man is stubborn and hardhearted and wants to do things his own way. He would rather take his chances with God and doing good deeds, relying on his own righteousness to get into heaven. Ignoring Jesus is mans' greatest mistake!
A lot of religions focus on God and merely "incorporate" Jesus. There is ONLY ONE way to reach God, which is why Jesus said, "I am THE way, THE truth and THE life; no man cometh unto the Father, but by ME." (John 14:6)