Why only few people allowed to be heaven? many christians go to hell?

Anybody, even the devil himself, can cast out devils, prophecy, and do so-called miracles in the name of Jesus. And many do it in order to mock Christianity. True Christians, those who have confessed with their mouths that Jesus Christ is their Lord and that God raised him from the dead, will have eternal life in the presence of both God and Jesus Christ. There is no limit to the number of people who can have that. You need to read the scriptures in context and in Matthew it is talking about false prophets.