I think little_socretes is correct:
The Bible is VERY clear Christians eat the bread and wine in remembrance to him. It IS the new convenient. It takes the place of Passover for Christians.
If you partake you are Christian.... if you don't you aren't.
Jesus himself, the actual MEDIATOR of the New Covenant states the ONE requirement for acceptance into the New Covenant (for forgiveness of sins) :
John 11: 25 - Jesus said unto her, I am the resurrection, and the life: he that believeth in me, though he were dead, yet shall he live:
John 6: 47 Verily, verily, I say unto you, He that believeth on me hath everlasting life. (present tense)
John 7 : 37 - He that believeth on me, as the scripture hath said, out of his belly shall flow rivers of living water.
Romans 10: 9 -13 - That if thou shalt confess with thy mouth the Lord Jesus, and shalt believe in thine heart that God hath raised him from the dead, thou shalt be saved.For with the heart man believeth unto righteousness; and with the mouth confession is made unto salvation. For the scripture saith, Whosoever believeth on him shall not be ashamed. For there is no difference between the Jew and the Greek: for the same Lord over all is rich unto all that call upon him. For whosoever shall call upon the name of the Lord shall be saved.
I guess for the sake of argument there is such a thing as unsaved Christians. However, I think for all practical purposes that only a saved Christian could be called a Christian.
The requirement for being a saved Christian or a real Christian if you like, is whether or not a person believes Jesus. This seems really simple. But, where people get into trouble is when they believe someone else over Jesus, or alongside Jesus.
For instance, when a person believes their religious teachers over what Jesus taught.... like participation in the Lord's Supper for example, they are really proving that their belief is primarily in someone else. Or, for example if they believe Mary or the Pope or their Church can provide Salvation ....then, in any of these kinds of instances they are proving that their belief is not on, or in Jesus, but some other.
That therefore nullifies the contract since the ONE requirement for Salvation is lacking.
When I used to go out in filed service, I used to mock Christians for saying that all you had to do was believe in Jesus to be saved. It turns out they were correct. However, they were not talking about the easy believism I had imagined.
It is not quite as easy as it sounds to believe in Jesus to the exclusion of all others, and irregardless of its cost.