If a person is disfellowshiped at a congregation, then how can that person biblically worship God? How does a person know that they have been disfellowshiped? Today's churches seem to practice no visible discipline, but many are treated as if they have been disfellowshiped. It seems the decision is made in secret among the accepted members, but the one disfellowshiped is never told. He only knows he has been placed in a uncomfortable position. I thought that for the Lord's Supper to be acceptable to the Lord those partaking are to be in communion with each other lest they bring damnation to their own souls.
In order to answer your question, we must first examine and understand what is meant by "fellowship," then we will be better able to discuss the concept of disfellowship.
Fellowship refers to having something in common or something shared between a group of individuals. For example, men who work together in a business are partners or in fellowship with each other. "So they signaled to their partners in the other boat to come and help them" (Luke 5:7). Sharing a common experience can also create a fellowship, such as soldiers who went through a war together or Christians who suffered persecution together. "I, John, both your brother and companion in the tribulation and kingdom and patience of Jesus Christ" (Revelation 1:9). Holding a common set of beliefs also creates a fellowship. "Those who have believers as their masters must not be disrespectful to them because they are brethren, but must serve them all the more, because those who partake of the benefit are believers and beloved" (I Timothy 6:2). And, when a person shares his possessions with another, he creates a fellowship with the one whom he is aiding. "For it pleased those from Macedonia and Achaia to make a certain contribution for the poor among the saints who are in Jerusalem" (Romans 15:26). "Nevertheless you have done well that you shared in my distress. Now you Philippians know also that in the beginning of the gospel, when I departed from Macedonia, no church shared with me concerning giving and receiving but you only" (Philippians 4:14-15).
In each of the verses cited in the previous paragraph, the words highlighted in bold print come from the Greek words dealing with fellowship. Fellowship is expressed in a variety of ways, but the foundation for fellowship is always that those involved share something in common with one another. The basis for Christian fellowship is the fellowship each Christian has with God. "That which we have seen and heard we declare to you, that you also may have fellowship with us; and truly our fellowship is with the Father and with His Son Jesus Christ" (I John 1:3). However, to have fellowship with God, we must have something in common with God. "This is the message which we have heard from Him and declare to you, that God is light and in Him is no darkness at all. If we say that we have fellowship with Him, and walk in darkness, we lie and do not practice the truth. But if we walk in the light as He is in the light, we have fellowship with one another, and the blood of Jesus Christ His Son cleanses us from all sin" (I John 1:5-7). In order for us to share God's light, we must practice the truth and obey God's commands. "Now by this we know that we know Him, if we keep His commandments. He who says, "I know Him," and does not keep His commandments, is a liar, and the truth is not in him. But whoever keeps His word, truly the love of God is perfected in him. By this we know that we are in Him. He who says he abides in Him ought himself also to walk just as He walked" (I John 2:3-6).
For His part, God went out of His way to share life with us. Jesus left heaven to share our earthly experience. "Inasmuch then as the children have partaken of flesh and blood, He Himself likewise shared in the same, that through death He might destroy him who had the power of death, that is, the devil" (Hebrews 2:14). "Therefore, in all things He had to be made like His brethren, that He might be a merciful and faithful High Priest in things pertaining to God, to make propitiation for the sins of the people. For in that He Himself has suffered, being tempted, He is able to aid those who are tempted" (Hebrews 2:17-18). "For we do not have a High Priest who cannot sympathize with our weaknesses, but was in all points tempted as we are, yet without sin" (Hebrews 4:15). Hence, faithful Christians have fellowship with God, the Father, and His beloved Son.
Because Christians share a common love for God and His word that love becomes the basis for fellowship between Christians. "Therefore, holy brethren, partakers of the heavenly calling" (Hebrews 3:1). No longer do Christians view themselves as separated by race or nationality. In Christ Jesus we become one people. "For you are all sons of God through faith in Christ Jesus. For as many of you as were baptized into Christ have put on Christ. There is neither Jew nor Greek, there is neither slave nor free, there is neither male nor female; for you are all one in Christ Jesus" (Galatians 3:26-28).
The existence of this fellowship is then expressed by the things we do together as Christians. For example, our weekly coming together to partake of the Lord's Supper is an expression of our common bond. "The cup of blessing which we bless, is it not the communion of the blood of Christ? The bread which we break, is it not the communion of the body of Christ? For we, though many, are one bread and one body; for we all partake of that one bread" (I Corinthians 10:16-17). Because of our love for the word of God, we join together in walking by the same rule. "Nevertheless, to the degree that we have already attained, let us walk by the same rule, let us be of the same mind" (Philippians 3:16). "God is faithful, by whom you were called into the fellowship of His Son, Jesus Christ our Lord. Now I plead with you, brethren, by the name of our Lord Jesus Christ, that you all speak the same thing, and that there be no divisions among you, but that you be perfectly joined together in the same mind and in the same judgment" (I Corinthians 1:9-10). In spreading the good news to the world, we again join in a common effort. "I thank my God upon every remembrance of you, always in every prayer of mine making request for you all with joy, for your fellowship in the gospel from the first day until now" (Philippians 1:3-5).
Fellowship is also expressed between Christians when we agree about common points and hold to a common plan. "When James, Cephas, and John, who seemed to be pillars, perceived the grace that had been given to me, they gave me and Barnabas the right hand of fellowship, that we should go to the Gentiles and they to the circumcised" (Galatians 2:9). Even when a Christian is unable to personally go and teach, his aid to those who are teaching is a sharing in the effort. "Nevertheless you have done well that you shared in my distress. Now you Philippians know also that in the beginning of the gospel, when I departed from Macedonia, no church shared with me concerning giving and receiving but you only. For even in Thessalonica you sent aid once and again for my necessities" (Philippians 4:14-16). "If we have sown spiritual things for you, is it a great thing if we reap your material things? If others are partakers of this right over you, are we not even more? Nevertheless we have not used this right, but endure all things lest we hinder the gospel of Christ. Do you not know that those who minister the holy things eat of the things of the temple, and those who serve at the altar partake of the offerings of the altar? Even so the Lord has commanded that those who preach the gospel should live from the gospel" (I Corinthians 9:11-14).
Ideally, a local congregation is a community of believers bound by their common love for God and their joint obedience to His word. It would be composed of only those who are being saved by our Lord God. I'm forced to say "ideally" because when it comes to the fellowship of the local congregation, people are involved, and people make mistakes. The Bible tells us of congregations who excluded those that should have been a part of their membership. "I wrote to the church, but Diotrephes, who loves to have the preeminence among them, does not receive us. Therefore, if I come, I will call to mind his deeds which he does, prating against us with malicious words. And not content with that, he himself does not receive the brethren, and forbids those who wish to, putting them out of the church" (III John 9-10). However, more common are the churches who accept those who are not in fellowship with God. The congregation at Corinth accepted a member who was guilty of fornication (I Corinthians 5:1-2, 6-7). They weren't the only ones guilty of welcoming sinners in their sin. "But I have a few things against you, because you have there those who hold the doctrine of Balaam, who taught Balak to put a stumbling block before the children of Israel, to eat things sacrificed to idols, and to commit sexual immorality. Thus you also have those who hold the doctrine of the Nicolaitans, which thing I hate" (Revelation 2:14-15). Because the basis of fellowship between Christians is the Christian's fellowship with God, a sinner cannot legitimately be a part of a congregation. The sinner has broken his relationship with God, which in turn undermines his relationship with followers of God. "Do not be unequally yoked together with unbelievers. For what fellowship has righteousness with lawlessness? And what communion has light with darkness? And what accord has Christ with Belial? Or what part has a believer with an unbeliever? And what agreement has the temple of God with idols? For you are the temple of the living God. As God has said: "I will dwell in them And walk among them. I will be their God, And they shall be My people." Therefore "Come out from among them And be separate, says the Lord. Do not touch what is unclean, And I will receive you."" (II Corinthians 6:14-17).
A church has a responsibility to manage its membership. It should welcome into her number those who are faithful followers of Christ, and it should reject those who have rejected Christ and are following after the world. Joining a congregation is not simply showing up for services. Before Saul's conversion was well know, he sought to join with the brethren, but they initially rejected him until someone they trusted vouched for him. "And when Saul had come to Jerusalem, he tried to join the disciples; but they were all afraid of him, and did not believe that he was a disciple. But Barnabas took him and brought him to the apostles. And he declared to them how he had seen the Lord on the road, and that He had spoken to him, and how he had preached boldly at Damascus in the name of Jesus. So he was with them at Jerusalem, coming in and going out" (Acts 9:26-28). Likewise, the removal of membership is not something done quietly on the side. Corinth was told to withdraw from a fornicator in their midst at the next worship service. "In the name of our Lord Jesus Christ, when you are gathered together, along with my spirit, with the power of our Lord Jesus Christ, deliver such a one to Satan for the destruction of the flesh, that his spirit may be saved in the day of the Lord Jesus" (I Corinthians 5:4-5). The separation extends beyond just the worship service. "But now I have written to you not to keep company with anyone named a brother, who is sexually immoral, or covetous, or an idolater, or a reviler, or a drunkard, or an extortioner--not even to eat with such a person" (I Corinthians 5:11).
You initially asked how a withdrawn from person can worship God. If a congregation has correctly done their duty, then their withdrawal is a public acknowledgment that the person withdrawn from is no longer in fellowship with God. In other words, a person who is in sin is unable to worship God because his sins places a barrier between him and God (Isaiah 59:1-2; I John 1:6). The congregation is not preventing a person from worshiping, they are acknowledging that a person's sins is preventing him from worshiping. To correct the situation, the sinning person needs to fix his relationship with God and then his relationship with his brethren can be repaired. "If we confess our sins, He is faithful and just to forgive us our sins and to cleanse us from all unrighteousness" (I John 1:9). The man whom Paul told the Corinthians to withdraw from turned from his sins. Paul then urges the Corinthians to accept the man back into their fold. "This punishment which was inflicted by the majority is sufficient for such a man, so that, on the contrary, you ought rather to forgive and comfort him, lest perhaps such a one be swallowed up with too much sorrow. Therefore I urge you to reaffirm your love to him." (II Corinthians 2:7-9).