The term Christianity seems to imply a religious system in the same way that Islam and Buddhism are religious systems. Within religious systems are core beliefs, along with codes, rules, and standards that must be mastered in order to achieve a desired end. Christianity does not fit that definition and therefore the term can be slightly misleading.
Jesus did not come into the world to start another religion. There were already plenty of religions (see Acts 17:22–23), including Judaism, which had begun as a relationship with Almighty God (Leviticus 20:12) but had deteriorated into another religious system on par with idol worship (Matthew 15:8). Jesus came to bear witness to the truth (John 18:37), to seek and to save the lost—those separated from God by their sin (Luke 19:10)—and to “give his life as a ransom for many” (Mark 10:32). With that said, those who follow Christ do share some core beliefs.
Biblically speaking, Christians are those who are forgiven of their sins and who have entered a personal relationship with Almighty God through faith in Jesus Christ (Ephesians 2:8–9; Romans 10:9–10). In order to become a Christian, a person must fully accept as part of his or her own personal worldview the following core beliefs:
• Jesus is the Son of God and is equal with God (John 1:1, 49; Luke 22:70; Mark 3:11; Philippians 2:5–11)
• Jesus lived a perfect, sinless life (Hebrews 4:15; John 8:29)
• Jesus was crucified to pay the penalty for our sins (Matthew 26:28; 1 Corinthians 15:2–4)
• Jesus rose from the dead (Luke 24:46; Mark 16:6)
• We are saved by the grace of God; that is, we cannot add to or take away from Christ’s finished work on the cross as full payment for our sin (Ephesians 2:8–9)
It could be argued that belief in the inerrancy of God’s Word is also a core belief of Christianity because, if the Bible’s veracity is suspect, then all we know about God is in doubt. Saving faith is inextricably linked to the Word of God: “Faith comes from hearing the message, and the message is heard through the word about Christ” (Romans 10:17).
But the mental acceptance of the above points of doctrine is only the framework around which salvation occurs. Faith is more than intellectual assent, and mentally agreeing with the core beliefs of Christianity does not equal entrance into God’s kingdom. Even Satan and the demons know certain things about God (James 2:19). We can mentally agree with facts without making those facts the centerpiece of our lives.
Can a person be saved without holding to the core beliefs of Christianity? No. But along with accepting as true those core beliefs must be a spiritual transformation. Jesus said that in order to inherit eternal life one must be “born again” (John 3:3). To be born again is a work of the Holy Spirit in the heart of a repentant sinner. Just as a mother in labor does all the work in bringing forth a new life, so the Holy Spirit does the work in transforming a sinner into a new creature (2 Corinthians 5:17). This process begins when God draws a heart through conviction of sin and hope of forgiveness (John 6:44). When we surrender to God and repent of our sin (Acts 2:38), God applies the blood of His own Son to our account and cancels the debt we owe Him (Colossians 2:14). By this act of transference, God pronounces us “not guilty”; that is, He justifies us (Romans 4:5). Salvation is a divine exchange: Jesus becomes our sin so that we can become His perfection (2 Corinthians 5:21). This is the gospel at the very core of Christianity.