Not all that claim they are Christians are. John 3:3 says: Except a man be born again, he cannot see the kingdom of God. Being born again is when you deny yourself and accept Christ. You die to the old sinful nature and are birthed into the family of God. In order to go to Heaven you must be born again. A true Christian repents, takes up his cross daily and follows Christ. A person cannot simply say they are a Christian then continue in sin without evidence of repentance.
True repentance is turning from your sins; trying to live a life well pleasing to God. A Christian will have some fruits or evidence of their faith in God. Examples might be: attending church, praying, leading others to Christ, refraining from doing things they once did. They no longer go to bars and hang out. They no longer stop at the alcohol store and buy liquour.
A Christian tries to show Christ in their life. They don’t hang around others who are living in sin, talking filthy, gambling. They don’t support things that God hates. Examples is: homosexuality, pride, forwardness, filthy jesting, adultery, etc… The Bible plainly tells us things to avoid. Mark 7:21,22 says: For from within, out of the heart of men, proceed evil thoughts, adulteries, fornications, murders, Thefts, covetousness, wickedness, deceit, lasciviousness, an evil eye, blasphemy, pride, foolishness:
Romans 1:29-31 says: Being filled with all unrighteousness, fornication, wickedness, covetousness, maliciousness; full of envy, murder, debate, deceit, malignity; whisperers, Backbiters, haters of God, despiteful, proud, boasters, inventors of evil things, disobedient to parents, Without understanding, covenantbreakers, without natural affection, implacable, unmerciful:
You may ask what it means to be born again. Jesus talks about it in John chapter 3. Jesus answered and said unto him, Verily, verily, I say unto thee, Except a man be born again, he cannot see the kingdom of God. Nicodemus saith unto him, How can a man be born when he is old? can he enter the second time into his mother’s womb, and be born? Jesus answered, Verily, verily, I say unto thee, Except a man be born of water and of the Spirit, he cannot enter into the kingdom of God. That which is born of the flesh is flesh; and that which is born of the Spirit is spirit. Marvel not that I said unto thee, Ye must be born again. The wind bloweth where it listeth, and thou hearest the sound thereof, but canst not tell whence it cometh, and whither it goeth: so is every one that is born of the Spirit (John 3:3-8).
Romans 1:22,23 tells us more about being born of the incorruptible seed which is of God. Seeing ye have purified your souls in obeying the truth through the Spirit unto unfeigned love of the brethren, see that ye love one another with a pure heart fervently: Being born again, not of corruptible seed, but of incorruptible, by the word of God, which liveth and abideth for ever.