What does it mean when the church withdraws fellowship?

1) IT MEANS that the individual has either been engaged in sin that is unrepented of, or, is still engaged in sinful activity. This places that individual as one who is out of fellowship with the Lord. As the Lord's body, we must discern and judge by the word of God of such a state of one's soul, and acknowledge that state by withdrawing our fellowship with such an individual.
1Cor 5:1-13 / 2Jhn 1:9-11 / Mth 18:15-20 / Titus 3:10 / Rev 2:14-16

2) IT MEANS that the individual's brothers and sisters in Christ love and care enough about the individual that they would engage in such an emotionally trying disciplinary act with the express reason being the restoration of the erring one,s soul.
Jms 5:19-20 / Gal 6:1 / 2Cor 2:3-11

3) IT MEANS that the Elders take seriously their responsibility of those souls under their watch. The Elders know that they will have to give an account for each soul that is lost while under their care.
Mth 18:10-14 / Heb 13:17

4) IT MEANS that the congregation believes the Word of God and trusts that God's ways are the best ways, even His plan for church discipline.
Prv 14:12 / Jer 10:23 / 2Thes 3:6-15

5) IT MEANS that the door of fellowship IS shut and locked, but, can always be opened with a "key" of true repentance. This "key" may be obtained through the individuals own study, or, by studying with any of the individual's brethren (we are STILL brethren), coming to the knowledge of his / her eternal state, and taking the necessary steps towards restoration.
The door is never closed permanently except at death.
2Cor 13:5 / 2Thes 3:15 (see above link) / Jms 5:19-20 (see above link) / 2Pet 3:7-18

6) IT MEANS that every reasonable effort has been exhausted in communicating to the individual that they are walking disorderly and contrary to the word of God. They have been given the opportunity to study any relevant matters and have either chosen not to study, or, have studied but have chosen not to repent and return to the fold.
Rev 2:21 / 2Pet 3:1

7) IT MEANS that the congregation loves and cares so much for Christ's church, that they strive to keep her pure.
Eph 5:27 / 2Pet 3:14 (see above link)

Is "Forsaking the assembly" Grounds For Disfellowship?

Some within the church are of the mind set that you can't withdraw fellowship from those who have "quit the church". They say it is akin to firing someone who has quit their job. First of all, the Lord's church is not a job. It is a kingdom with a King. The Bible alludes to only two kingdoms. You are either in the Lord's, or Satan's. If you "quit" the Lord's, than guess what, you are in Satan's kingdom (Mt 12:30, Rms 6:16). Are we willing to fellowship those in Satan's kingdom? I don't think so! Paul likens it to being in the military (Phil 2:25, 2Tim 2:3-4). You can not just "quit" the military. But for the sake of argument, let's look at it in the context of a job. Most employers have rules and regulations, even for quitting. If one day you just stop showing up for work, most employers contact you and fire you in some manner, whether you think you quit or not!

Another argument is that the use of Paul's term "disorderly" in 2Thes 3:4-6 has only to do with those who are busybodies and will not work. I want to start first with reading Heb 10:22-29:
Heb 10:22-29 = 22)Let us draw near with a true heart in full assurance of faith, having our hearts sprinkled from an evil conscience and our bodies washed with pure water. 23)Let us hold fast the confession of our hope without wavering, for He who promised is faithful. 24)And let us consider one another in order to stir up love and good works, 25)Not forsaking the assembling of ourselves together, as is the manner of some, but exhorting one another, and so much the more as you see the Day approaching. 26)For if we sin willfully after we have received the knowledge of the truth, there no longer remains a sacrifice for sins, 27)But a certain fearful expectation of judgment, and fiery indignation which will devour the adversaries. 28)Anyone who has rejected Moses' law dies without mercy on the testimony of two or three witnesses. 29)Of how much worse punishment, do you suppose, will he be thought worthy who has trampled the Son of God underfoot, counted the blood of the covenant by which he was sanctified a common thing, and insulted the Spirit of grace?

In answering our question "is forsaking the assembly grounds for disfellowship?", one must first decide if, according to Hebrews chapter 10, deliberately missing a series of worship assemblies is a sin against God?

Before we answer, let's look a little deeper and see if God requires us to be a part of a local congregation:

1) God, through His word, assumes and implies that a believer will be part of a local congregation of the Lord s church (1Cor 11:17-34). A body (church) can not function unless there is unity of operation among it's members. God never calls upon his children to be "Lone Rangers", but to be unified with other believers as a fighting unit against the wiles of Satan (2Cor 10:3-6). (See also 1Cor 1:10, 12:12-27, Eph 1:22-23, 4:1-5, 4:11-16)

#2) The local congregation is the only place we can fulfill a majority of our spiritual needs and requirements: Fellowship, encouragement, accountability (including discipline), prayers, benevolence, edification, communion, worship, motivation, giving, preaching, and many others. (See Rms 12:3-13, 1Cor 11:18-20, 16:1-2, Heb 10:24-29, Eph 4:1-5, 11-16)

#3) The Lord expects his disciples to be part of the local congregation under an Eldership (See Acts 20:28, 1Thes 5:11-14, Titus 1:5, Heb 13:17).

#4) It is also interesting to note that when God put forth His New Testament, a large portion was distributed through epistles to local congregations. Note especially His final revelation (The book of Revelations), which was given as a message through specific congregations.

With all of this in mind, I think it would be safe to say that yes, God most certainly wants His children to be part of a local congregation of His church. That being the case, and with regards to Hebrews 10:22-29, I submit to you that it is a most faithful and trustworthy saying that says "any brother or sister in Christ, who deliberately stops attending the local congregation's worship assemblies, is in a lost and sinful state before God Almighty".

So, seeing that a brother or sister IS committing sin when they forsake the assembly of the church, would they not then be guilty of walking disorderly? Let's define "disorderly" as it is used in 2Thes 3:4-6: 2Thes 3:4-6 4)And we have confidence in the Lord concerning you, both that you do and will do the things we command you. 5)Now may the Lord direct your hearts into the love of God and into the patience of Christ. 6)But we command you, brethren, in the name of our Lord Jesus Christ, that you withdraw from every brother who walks disorderly and not according to the tradition which he received from us.

Strong's #814 = "disorderly" (Greek: ataktws)
1) disorderly, out of ranks (often so of soldiers)
2) irregular, inordinate, immoderate pleasures
3) deviating from the prescribed order or rule

If ANY and ALL sins do not fit into the meaning of "walking disorderly", as used by Paul in 2Thes 3:4-6, then I am at a loss as to the method of logic and reasoning that draws such a conclusion.
Consider also the following scriptures:
1Jhn 3:4 = Whosoever committeth sin transgresseth also the law: for sin is the transgression of the law.
2Jhn 1:9-11 = 9)Whoever transgresses and does not abide in the doctrine of Christ does not have God. 10)He who abides in the doctrine of Christ has both the Father and the Son. 11)If anyone comes to you and does not bring this doctrine, do not receive him into your house nor greet him; For he who greets him shares in his evil deeds.

The Lord's church (each and every faithful Christian) MUST disfellowship themselves from any and all unfaithful brethren, or they WILL be held accountable by God as per His word (Jhn 12:48). And PLEASE remember the two ultimate goals are to bring a sinner back from death (Jms 5:19-20), and, to keep the church pure (1Cor 5:4-8)! Are there any more lofty and noble goals?