The reason to celebrate “the Lord’s Supper” (1 Corinthians 11:20 NIV) is because Jesus Christ, the Son of God, commanded that his disciples should. Notice:

“And he took bread, gave thanks and broke it, and gave it to them, saying, ‘This is my body given for you; do this in remembrance of me.’ In the same way, after the supper he took the cup, saying, ‘This cup is the new covenant in my blood, which is poured  out for you'”—Luke 22:19,20 NIV

“For I received from the Lord what I also passed on to you. The Lord Jesus, on the night he was betrayed, took bread, and when he had given thanks, he broke it and said, ‘This is my body, which is for you; do this in remembrance of me. ‘In the same way, after supper he took the cup, saying , ‘This cup is the new covenant in my blood; do this, whenever you drink it, in remembrance of me.’ For whenever you eat this bread and drink this cup, you proclaim the Lord’s death until he comes”—1 Corinthians 11:23-26 NIV

In both of these accounts, Jesus is quoted as telling his disciples to ‘eat the bread and drink the wine’ “in remembrance of me.” Jesus is speaking metaphorically, not literally, when he says, “This is my body,” and “This cup is the new covenant in my blood.”  Catholics claim that the bread is changed into Jesus’ body, and the wine is changed into Jesus’ blood at their Mass. Some others teach that the bread and wine become mixed with Jesus’ body and blood during their communion service. Both of these teachings are “false doctrines” that “go beyond what is written in Scripture” (1 Timothy 1:3,4 NIV; 1 Corinthians 4:6 GWT). 

The purpose of the celebration is explained to be that “you proclaim the Lord’s death until he comes” (1 Corinthians 11:26 NIV). Indeed, “By this gospel you are saved, if you hold firmly to the word . . . as of first importance: that Christ died for our sins according to the Scriptures” (1 Corinthians 15:2,3 NIV). The point is that “the Lord’s Supper” is celebrating the death of Jesus Christ for our (humanity’s) sins. 

There are no exact, or precise, instructions given in the Bible as to exactly when, or how often, “the Lord’s Supper” should be celebrated. It is obvious, however, that among early Christians, it was “when you come together” (1 Corinthians 11:20 NIV), “when you meet together” (NLT), that is, as a group, either an entire local church, or as small groups of Christians.

God deals with people through covenants. 

“For there is one God and one mediator between God and mankind, the man Jesus Christ, who gave himself as a ransom for all people”—1 Timothy 2:5,6 NIV

“Christ is the mediator of a new covenant, that those who are called may receive the promised eternal inheritance–now that he has died as a ransom to set them free from the sins committed under the first covenant”—Hebrews 9:15 NIV

To be forgiven of sins and qualify for eternal life, one must be in the “new covenant” mediated by Christ. Being in that “new covenant” is symbolized by partaking of the wine and bread at “the Lord’s Supper” (1 Corinthians 11:20 NIV).

The first step toward entering the “new covenant” is to: “Repent and be baptized, every one of you, in the name of Jesus Christ for the forgiveness of your sins” (Acts 2:38 NIV). A Christian must continue to confirm he/she is in the “new covenant” by celebrating “the Lord’s Supper.”

But “everyone ought to examine themselves before they eat of the bread and drink of the cup. For those who eat and drink without discerning the body of Christ eat and drink judgment on themselves” (1 Corinthians 11:28,29 NIV). 

What does this mean? “Whoever eats the bread or drinks the cup of the Lord in an unworthy manner will be guilty of sinning against the body and blood of the Lord” (1 Corinthians 11:27 NIV). It could possibly mean something like celebrating “the Lord’s Supper” ( compare Hebrews 11:26 NIV) while living in unrepentant sin. God is the ultimate judge, of course, but we should be sure that we’re not living in unrepentant sin. If we are, we had best not partake of the bread and wine until we “Repent . . . and turn to God, so that your sins may be wiped out, that times of refreshing may come from the Lord” (Acts 3:19 NIV). The principle: “To obey is better than sacrifice” (1 Samuel 15:22) certainly applies. 

To ‘eat the bread and drink the wine’ “in an unworthy manner” may, more likely, mean participating in it without thinking of its serious and sacred meaning, which is honoring Jesus’ sacrificial death. In one sense, no one is really worthy to take “the Lord’s Supper”, because we’re all sinners saved by grace. But this is exactly why we should prepare ourselves through self-examination, confession of sin, and resolving differences with others. Jesus would not have commanded his imperfect followers to “do this in remembrance of me” if no one could qualify to do so.

It is obvious from the scriptures that only baptized believers who are in the “new covenant”, and not unbelievers, qualify to celebrate the Lord’s Supper.