Unfortunately, it is impossible for us mortals to see this, leading to lots of debate about how to separate "true Christians" from the 90% or so of Americans who claim it as their religion.
One of the identifying marks of a Christian is that they are generally happy, successful people. I do not mean successful in the financial sense of being CEOs of large companies -- many Christians are very poor and some are even bankrupt. I mean successful in the psychological self-actualization sense; these are people who are able to cope with life's up-and-downs; they strive for excellence at whatever they do; they have what Paul describes as an inner tranquility [Paul wrote numerous letters from prison, none of which complained about how unfair his incarceration was].
Verbally identifying "I am a Christian" does not guarantee that you are, but it is rude to doubt someone about this. Having an intellectual belief that God exists is not sufficient; you must also love Him. And the Bible is clear that we show our love for God by following his commands. None of us are perfect; all of us break God's commands (legalistic obedience isn't sufficient; we must follow the spirit of the law with our hearts as well), however true Christians have knowledge of God's forgiveness. He does not require perfection; merely a commitment to improve and acknowledgement of our failures.
Knowledge of the Bible is certainly an admirable trait, but is not absolutely required to be a true Christian. Very many early Christians were unable to read, and for many centuries the Bible was available only in Latin. Contrariwise, a great many atheists have read the Bible cover to cover. However, being a Christian does mean that you acknowledge the Bible as spiritual authority. Different Christians disagree on some interpretations of what the Bible means[especially on things in Genesis and Revelations], but if a clear teaching of the Bible contradicts a Christians personal moral code, the Christian is expected to abide by the Bible's teaching.
Public participation in Church activities is another trait which does not guarantee Christian salvation. Jesus had some of his harshest criticisms for the religious leaders of His day, and especially complained of people who prayed in public for the purpose of being seen praying. In fact, Jesus's advice on prayer is to "Pray in a closet". Christians are to have a personal connection to Deity, and not be a cog in a beaurocratic institution.
Advocacy of moral codes does not indicate Christianity. Certainly the Bible expresses a moral code which Christians should follow, and most Christians belief that life will be better for everyone if even non-Christians follow the behavior prescription and proscriptions in the Bible. However, a great deal of current moral harruanging is not based on the Bible. Many people calling themselves Christians are against all alcohol use, yet Jesus more than once turned water into wine. Contrariwise, Jesus makes it clear that anyone who divorces [for a reason other than adultery] commits adultery when they remarry-- and yet, a great many protestants give the church's blessing to this sin. So many moral codes advocated by self-identified Christians are not Bible-based, and many people other than self-identified Christians advocate various moral codes. However, to be a Christian is to acknowledge that there is sin, that some actions are required and some forbidden [and many others permitted], and that we voluntarily chose to follow God's moral code in preference to our own culture or intuition.
This list has turned more into a "Calling yourself a Christian does not make you one", which gets back to my original point; true Christians are identified -- but not to us-- by having the holy spirit in their hearts.
What a horrible load of BS. "Blessed are the poor in spirit". You are spouting a "theology of glory" and what you are advocating DOES usually imply that Christians will make money, be healthy, blah blah. Say, was John the Baptist a successful person by ANY human or psychological standard?