While anyone can claim to be a Christian, truly being a born-again believer in Christ is more than a simple statement. Because of the misunderstanding of what a Christian actually is, Christians that understand the difference in Christian association and really being a Christian have come up with the phrase "True Christians" to differentiate themselves from these "False Christians."
There are also two schools of thought on whether a Christian can lose his/her salvation. One group feels that a Christian can lose his/her salvation; another group feels that a Christian cannot lose his/her salvation. I have outlined below with Biblical references why I believe a Christian can never lose his/her salvation.
1) All who are truly Born Again will persevere to the end. References: John 6:38-40, John 10:27-29, Ephesians 1:13-14, etc.
2) Only those who persevere to the end have been truly Born Again. References: 1 Peter 1:5, John 8:31-32, Matthew 10:22, Colossians 1:22-23, Hebrews 3:14, 1 John 2:19, etc.
3) Those who fall away may give many external signs of conversion. References: Galatians 2:4, 2 Corinthians 11:26, 2 Corinthians 11:15, Matthew 7:21-23, John 15:1-2,6, Hebrews 6:4-8, Matthew 3:8-10, Matthew 7:15-20, Matthew 12:33-35, etc.
4) So what can give a believer genuine assurance? Each person can answer for himself/herself:
a) Do I have a present trust in Christ for Salvation? (Colossian 1:23, Hebrews 3:14, Hebrews 6:12, etc.)
b) Is there evidence of a regenerating work of the Holy Spirit in my heart? (Romans 8:15-16, 1 John 4:13, Galatians 5:22, Matthew 7:16-20, 1 John 2:23-24, 1 John 4:6, John 15:4,7, 1 John 2:4-6, etc.)
c) Do I see a long-term pattern of growth in my Christian life? (2 Peter 1:5-7, 2 Peter 1:10, 1 Peter 1:5, John 6:40, etc.)
If you don't answer "Yes" to each of these questions in #4 above, then you were never a Christian. If you answer "Yes" to each of these questions in #4 above, then you are a Christian. For those that cannot answer "Yes" to the questions above, I pray that you would come to Christ today. It is not too late as long as you have breath in you. Repent, and trust Christ to be your personal Lord and Savior. He loves you and wants to have an intimate, personal (parent-child) relationship with you.