What does it mean to be a true Christian?

TL;DR:

A true Christian is one who follows Christ by accepting Him as Savior. A true Christian loves God, loves others, and reflects His love and character to others through works enabled by the indwelling Holy Spirit.

what does the bible say?

The Bible records the first use of the word “Christian” in Acts 11:26. Prior to that, Christ’s followers were considered as a sect of Judaism called “The Way” (Acts 9:1–2). Though the word “Christian” is not mentioned often in the Bible, Scripture indicates the traits that define a true Christian. Two of these are love of God and love of others (Matthew 22:36–40; Mark 12:28–31; Luke 10:25–28). Loving God and others also undergird the Mosaic Law (Deuteronomy 6:5; Leviticus 19:18). Jesus reiterated these same requirements for those who follow Him (Matthew 22:38–40; Mark 12:28–31; Luke 10:25–28). Besides Christians being recognized by their love for God and others, Scripture presents other markers of true Christianity: belief in Christ as the Messiah (1 John 5:1) and the presence of the indwelling Holy Spirit (Matthew 7:15–20; Galatians 5:22–24). The latter shouldn’t be mistaken for works-based theology, though. Scripture makes it clear that Christian behavior is an outworking of faith, not a cause of salvation (Ephesians 2:8–10; Philippians 2:12–13). True Christians follow Christ in their hearts and lives.

from the old testament

Though there is no Christianity without Christ, the principles on which Christianity is based are seen in the Old Testament. For instance, Deuteronomy 6:5 emphasizes love of God: “You shall love the Lord your God with all your heart and with all your soul and with all your might.” In the gospels, Jesus calls this the “greatest commandment” (Matthew 22:38).
Love for others, another essential Christian trait, is also part of Old Testament law. Leviticus 19:18 says, “You shall not take vengeance or bear a grudge against the sons of your own people, but you shall love your neighbor as yourself: I am the Lord.” In Matthew 22:39, Jesus says this is the second greatest commandment.

from the new testament

In Luke 10:27–28, a young lawyer answers his own question to Jesus about how to inherit eternal life: “And he answered, ‘You shall love the Lord your God with all your heart and with all your soul and with all your strength and with all your mind, and your neighbor as yourself.’ And he [Jesus] said to him, ‘You have answered correctly; do this, and you will live.’” True Christians will love God and love others.
But genuine Christians must also believe in Christ as the Son of God and Savior. First John 5:1 says, “Everyone who believes that Jesus is the Christ has been born of God, and everyone who loves the Father loves whoever has been born of him.” One cannot be a real Christian without accepting Jesus as Messiah.
True Christians are indwelt by the Holy Spirit, and their lives manifest that, as indicated in Galatians 5:22–24: “But the fruit of the Spirit is love, joy, peace, patience, kindness, goodness, faithfulness, gentleness, self-control; against such things there is no law. And those who belong to Christ Jesus have crucified the flesh with its passions and desires.” Our good works do not save us, but they are the consequence of being saved. Real Christians are new creations, with new hearts and desires that cause them to pursue holiness and do good deeds out of love for God

implications for today

Some words don’t mean what they seem to. We drive on parkways but park in driveways. We eat something called a hamburger that contains no ham. And “rush” hour traffic is glacially slow. Sadly, the same can apply to those who call themselves “Christian.” “Christian” should mean “follower of Christ,” but sometimes, the name is applied to people simply because they attend church on Sundays and have a Jesus fish bumper sticker on their car. But the Bible tells us a true follower of Christ is someone who loves God, loves others, believes in Jesus as Savior, and whose life shows the influence of the indwelling Holy Spirit. As Paul says when defining what a real “Jew” is, “a Jew is one inwardly, and circumcision is a matter of the heart, by the Spirit, not by the letter” (Romans 2:29). How does Christ show up in your life? Do you immerse yourself in His Word to learn more about Him? Do you regularly reach out to Him in prayers of praise, thanksgiving, and supplication? Do you show others the love of Christ by telling them about Him, helping them, and overlooking offenses? Going to church doesn’t make us “Christian.” Neither do performative rituals, crosses on jewelry, or pious bumper stickers. Jesus alone saves. To those who believe that and have accepted Him into their hearts as Lord, He has given the right to “become children of God”—Christians (John 1:12). True Christians follow Christ in their hearts and lives.

understand

A true Christian loves God and others, reflecting Christ's love.
A true Christian believes in Jesus as the Savior.
A true Christian's life is transformed by the Holy Spirit, resulting in good works.

reflect

How does your love for God and others reflect your true identity as a Christian?
How has your belief in Jesus as the Savior changed the way you live your life?
How do you see the Holy Spirit working in your life, and how does it affect your actions and decisions?

engage

What does it look like to truly love God and love others in your daily life?
How do we distinguish between being a "cultural Christian" and a true Christian, and what role does the Holy Spirit play in that?
How can we encourage one another to live out the transformation brought about by the Holy Spirit?