Child of God or Child of the Devil?

Today many churches have embraced "easy-believism" - mental assent to all the facts about Jesus will get them to heaven. They say they believe, have faith in, or have put their trust in the following Scripture.
"GOD SO LOVED THE WORLD THAT HE GAVE HIS ONE AND ONLY SON THAT WHOEVER BELIEVES IN HIM WILL HAVE EVERLASTING LIFE."
-(JOHN 3:16)(NIV)

I think these people do believe everything about Jesus from His being deity, took on the form of man, was sinless, took on their sin, was punished, crucified, arose from the grave on the third day, is in heaven now, and will be the final judge of both the children of God and the children of the devil.
However, the demons also believe everything from Jesus incarnation to the fact he will be their final judge. When Jesus approached the demon possessed man, the demons said, "What do you want with us, son of God? Have you come to torture us before the appointed time?"
-(Matthew 8:29)(NIV)

In Matthew 7:21, at the final judgement, Jesus tells people who have been prophesizing in His name, casting out demons in His name and even doing miracles in His name, "Depart from me I never you!"
We know the demons are not going to heaven, but what is missing in the lives of the people who do miraculous things in Jesus name?
Furthermore, Jesus in three of His parables tells us about people that act like, think like, and believe they are Christians - children of God, but they are not.
Believing in Jesus means not only believing in what He did for us but what He said. Jesus says there are three other things we must do to become a child of God. Other Scriptures declare other requirements for becoming a child of God.
This book challenges us to examine ourselves to see if we have met and committed to all those requirements.