I wish it were that way, brother - I truly do. Unfortunately it is not enough to simply believe. James tells us that even the demons believe in God and tremble (James 2:19).
"You believe that there is one God. You do well. Even the demons believe-and tremble!"
Being a 'believer' as it is commonly used among Christians, isn't limited to belief in God.
I agree with you *wholeheartedly* that 'belief that there is one God' is not enough - every manner of heresy springs from "I believe in God' in which the speaker goes on to describe a god of their own making. From New Agers to devil worshipers. The broad way - which, as Scripture tells us, leads to destruction.
Believers, as commonly used amongst Christians, are those who believe in God AND, that Jesus - the Word came in the flesh, died on a cross for our sins, was resurrected on the 3rd day, ascended into heaven and sits at the right hand of the throne of God, from whence He will come to judge the quick and the dead. That Jesus is the Truth, the Way and the Life and that no man comes to the Father, except by Him. (I did this off the top of my head, so apologies if I left out something major).
Those who believe in the one true God, believe in Jesus Christ Whom He sent. But, then we have to determine whether or not that belief is in Jesus Christ as revealed in Scripture, or if they claim belief in a Jesus who is also of their own making.
Elvisman, I think it was you who said something the other day about heresies are usually rooted in an attempt to denigrate or denude any one of the Trinity. I paraphrased, but hope that I accurately represented what you said - because I absolutely agree with you if I understood you correctly.