Some might say it is primarily
- acting in obedience to God (going/serving in church)
- having the right doctrine
- having the right feelings toward God (experience)
- trying hard to follow God
These are all connected to true discipleship, but fail to get at the core of what being an actual disciple of Christ is. The core of what makes us a disciple is the Life of God in the soul of man. Many (I dare to say most) people who consider themselves Christians, consider themselves as such because they are generally "good" people and "try hard to obey". However, these notions of what it means to be a disciple deflate the reality of John 3:3 that "unless they are born again, they can't see the kingdom of God." The Gospel of Jesus Christ demands change. It is impossible to come to any true knowledge of God without a complete overhaul of one's nature. That's why being a disciple is more than just trying hard and attempting to be obedient to God's commands. We can't change ourselves and our attempts to do so always fail. We are only made disciples by the Life of God taking root in our souls, thus causing us to be born again.
The Apostle Paul writes, "Therefore, if anyone is in Christ, the new creation has come: The old has gone, the new is here! All this is from God, who reconciled us to himself through Christ..." (2 Corinthians 5:17). We see here, that this new life is only given by God. Moreover, this new life is supernaturally given through Christ. We are reconciled to God through our union with Christ. The only way for us to have a complete overhaul of our nature, and thus become disciples, is by Christ supernaturally causing us to be born again into new creations through His power, manifested in His law fulfilling life, sin defeating death, and life giving resurrection.
In other words, being united to Christ is what makes us His disciples. Not human effort, not behavior modification, and not a warm fuzzy feeling. It is the supernatural indwelling of God in the soul of the believer. This is called union with Christ, and it is the grounds for our
- Justification: "There is therefore now no condemnation for those who are in Christ Jesus" Romans 8:1
- Sanctification: "and from him you yourselves are in Christ Jesus, who became wisdom for us from God, and righteosness and sanctification and redemption." 1 Corinthians 1:30
- New Life: "But if Christ is in you, then even though your body is subject to death because of sin, the Spirit gives life because of righteousness." Romans 8:10
- Glorification: "God raised the Lord and will also raise us up by His power" 1 Corinthians 6:14
"Because I live, you also will live. In that day, you will know that I am in my Father, and you in me, and I in you." --John 14:20