A recent study has determined that there are now over 39,000 "Christian" denominations! That means there are probably over 39,000 "official" definitions of what it means to "act" like a Christian.
Phillip Gulley wrote in "What if the Church were Christian":
Sometimes when someone does something I don't agree with, I'll say, "They're not acting very Christian." What I really mean to say is they're not acting like I think a Christian should act. But they might be acting in a manner consistent with their understanding of Christianity. I don't get to define what Christianity should mean to them. We each get to do that for ourselves.
No one can say "you must believe this or you must believe that". We are free. The beliefs we choose have a profound effect on our lives. They can make the difference between a rich, full life that is wide and expansive and welcoming, or a mean, narrow life that is closed off and harsh and judgmental.
James Fowler said in his article, What it means to be a Christian:
There is much confusion among the general public, as well as the religious community, concerning what it means to be a "Christian."
Does it mean assenting to a particular belief-system?
Does it mean consenting to a prescribed morality pattern?
Does it mean changing and improving one's behavior?
Does it mean joining a church organization?
Does it mean practicing regular rituals of worship?
There is no physical or psychological procedure or formula that one must follow precisely in order to become a Christian. It is not effected by the physical procedures of walking down an aisle in response to an invitation, or holding up one's hand, or repeating a pre-worded "confession of faith," or being baptized with water, though those may be engaged in to indicate or accompany one's response to Jesus Christ. Neither do the psychological responses of mental assent to historical and theological tenets, or the subjective experiences of human emotions constitute the means and manner of responding to Christ.
Everything necessary for being and behaving as the Christian one has become is inherent within and derived from the One with whom we have spiritually identified and united, Jesus Christ. Being and living as a Christian is not a religious exercise of conformity to the example of the historic life of Jesus Christ, striving to be Christ-like. Attempts to pattern one's behavior after that of Jesus amount to nothing more than self-serving attempts to "parrot" or "ape" the behavior-pattern of another. The Christian life is not an imitation of Jesus, but the manifestation of His life and character. [His life through us]
Living the Christian life is not comprised of going through the motions of repetitive religious rituals. Nor is it the legalistic keeping of behavioral rules and regulations in conformity to an ethical morality. Ecclesiastical involvement is not the essence of Christian living either; not church attendance, participating in religious programs, or tithing ten-percent of one's income.
Being and behaving as a Christian is enabled and empowered by the grace of God in the dynamic of the life of Jesus Christ in the Christian. In His departing promise Jesus explained, "You shall receive power when the Holy Spirit has come upon you" (Acts 1:8). "God's grace is given according to the working of His power" (Eph. 3:7), providing "all sufficiency in everything" (II Cor. 9:8).
Therefore, consistent with our becoming a Christian, it is not what we do to behave and live as a Christian, but the recognition of the sufficiency of the life of Jesus Christ within us. "He who began a good work in you will perfect it until the day of Christ Jesus" (Phil. 1:6).
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Being a "Christian" is not about rules, rituals or religion. It is about a person, Jesus. It is about a relationship with Him. It is knowing that He is part of you and loves you no matter what you do or don't do.
It is not about receiving Him, but knowing that He has received us. It is not about believing in Him, but knowing He believes in us. It is not about asking for forgiveness, but knowing He has already forgiven us.
It is simply living in the truth that the Father, Son and Spirit love us. .