A “hypocrite” is someone who pretends to be something he is not. The Greek derivation of the word confirms this idea: one who is on the stage, an actor. A current rough equivalent is “poser”. We frown on hypocrisy because it is a kind of dishonesty. 

When you pray, you must not be like the hypocrites. For they love to stand and pray in the  synagogues and at the street corners, that they may be seen by others. (Matthew 6.5).

He began to say to his disciples, “Beware of the leaven of the Pharisees, which is hypocrisy.  (Luke 12.1).

Such teachings come through hypocritical liars, whose consciences have been seared as with a hot iron. (1 Timothy 4.2).

It is possible to act hypocritically without actually being a hypocrite. This is usually a case of “falling” into hypocrisy, maybe feeling some unease, but not being fully aware of acting inappropriately. Those who are hypocrites, in contrast, are committed to it, seeing it as a calculated advantage. In any case, when our hypocrisy comes to light, it is something we are to repent of. 

When Cephas came to Antioch, I [Paul] opposed him to his face, because he stood    condemned. For before certain men came from James, he was eating with the Gentiles; but  when they came he drew back and separated himself, fearing the circumcision party.And the   rest of the Jews acted hypocritically along with him, so that even Barnabas was led astray by  their hypocrisy. (Galatians 2.11-13).

The New Testament takes a similar approach to the term “sinner”. 

God demonstrates his own love for us in this: While we were still sinners, Christ died for us.  Since, therefore, we have now been justified by his blood, much more shall we be saved by   him from the wrath of God. ( Romans 5.8,9). Here, “sinners” is used to describe  Christians before they became Christians. 

Paul, an apostle of Christ Jesus by the will of God, To God’s holy people in Ephesus… (Ephesians 1.1). Here, God’s people are called holy.

The New Testament teaches that we are no longer sinners but saints. How can this be when we continue to struggle with sin? Paul himself struggled with sin. 

I do not understand my own actions. For I do not do what I want, but I do the very thing I hate. I have the desire to do what is right, but not the ability to carry it out. I do not do the good I want, but the evil I do not want is what I keep on doing. I see in my members another law waging war against the law of my mind and making me captive to the law of sin that dwells in my members. Wretched man that I am! Who will deliver me from this body of death? (Romans 7.15,18,19,23,24).

Even though Christians are still sinners, they are no longer called sinners. How does this make sense? First of all, by God’s grace, Christians are awarded Christ’s righteousness so, in God’s sight, we are pure. But even at the human level there is a profound difference. Sinners and hypocrites are comfortable with sinning and posing. Christians, in contrast, hate sin and hate hypocrisy, and battle daily to leave both behind. One embraces, the other disdains. Effectively, this means that Christians are the anti-hypocrites even if, like Paul Simon, they are sometimes “fakin’ it”.

It is not possible for the Church to be made up of hypocrites, since the Church is defined as those who believe in Jesus Christ as Lord. Faith in Christ is the critical concern for the Church, when it comes to hypocrisy, and the issue of concern when it comes to Communion.

So how does this bear on urging non-Christians to not take part in Communion? First of all, an exhortation is correct that informs non-Christians that their taking Communion would be hypocritical. Christ commanded his disciples to regularly observe Communion “in remembrance” of him. This remembrance is not something akin to remembering, say, State capitals. It is a call to think specifically about who Jesus is and what he has done. It is to remember that he proved his power over sickness, nature, and death; that he spoke pure truth; and that he lived a sinless life. More importantly, it is to remember that he went willingly to the cross, dying in order to deliver his people from their bondage to sin and death. His command also looked forward to his resurrection, which seemed to be the final proof the disciples needed to be convinced that Jesus was, himself, God. 

Therefore, those who participate in Communion ought to be those who are proclaiming their identity in Christ and their absolute trust in him, even as they proclaim their unity with all other believers, i.e., the Church. As a matter of integrity, persons who do not believe these things ought not participate in such a ritual.  An explanation that they should not participate on the basis that “the Church already has enough hypocrites,” is utterly confusing. If the Church is full of hypocrites, ritual hypocrisy would serve as an appropriate initiation rite. 

I don’t know the best words for discouraging unbelievers from taking the Communion elements. I’m sure it’s hard to do without talking for a long time. Here’s a stab at it: “Those who participate in Communion are proclaiming they are Christians. They are proclaiming that Jesus, alone, grants salvation; that he is Lord of all creation; that he is God. They are also proclaiming unity and commitment to all of God’s people, the Church. If you believe these things, please join with us in the Communion celebration. If you do not, we ask that you maintain your integrity and let the elements pass you by. This does not mean we do not love you; nor that you are of less value than those who do partake. You are welcome among us. We look forward in hope for the day when you, too, trust in Jesus and can rightfully join with us in the Communion ceremony.”