The Second Key: Church Discipline (Heidelberg Catechism, Lord's Day 31; Matthew 18:1-22) by Rev. Angus Stewart.
I. A Difficult Key
II. A Necessary Key
The Necessity of Christian Discipline (Rev. Ron Hanko)
One thing almost completely missing in the church today is biblical church discipline. It is an almost unheard of for anyone to be excommunicated from the church, except for gross sin (they are not always disciplined even for that). People who live unchristian lives are allowed to remain in the church as members. Unbelievers serve in church offices. Ministers are allowed to preach anything and everything, no matter how unbiblical it may be. Sin, unbelief, backsliding, disobedience are rarely even rebuked.
Especially this is true of many thing which are counted "little" sins, but are especially destructive when allowed to remain unrebuked and unchecked in the church. It would be an unusual thing for sins such as speaking evil of others and gossiping to be rebuked, or for sins such as envy, hatred, or strife to be named as sin, yet they are destructive both of the church and of the service of God (Prov. 26:17-28; Matt. 5:21-24). They are like the little foxes that spoil the vines (Song 2:15).
The result of this lack of discipline is that sin in all its ruinous power flourishes and grows in the church, so that eventually the church is ruined. As the Word reminds us when speaking of sin in the church of Corinth: "A little leaven leaveneth the whole lump" (I Cor. 5:6). Indeed, even the lack of first love, though everything else was in place, brought on the church of Ephesus the threat of having its candlestick removed (Rev. 2:1-7).
Christian discipline reaches its conclusion in censure and excommunication. In spite of the fact that such action is not pleasant, it is of the utmost importance for the safety and well-being of the church, and so Scripture speaks of it often (Matt. 18:15-17; I Cor. 5:1-13; I Tim. 1:19-20; II Thess. 3:14-15; Rev. 2:2).
In Scripture this aspect of Christian discipline is described in terms of delivering a person to Satan (I Cor. 5:5; I Tim. 1:20), of excluding him or her from fellowship (Matt. 18:17; II Thess. 3:14), especially from the fellowship of the Lord's Supper (I Cor. 5:11, 13). In some cases at least it involves an actual trial of those who have sinned (Rev. 2:2).
That Christian discipline involves such extreme measures is probably the chief reason it is seldom carried out. Nevertheless, it is important not only for the well-being of the church, but for the salvation of the sinner. I Corinthians 5:5 (cf. also I Thess. 3:14), having described discipline in the strongest possible terms, insists that its main purpose is "the destruction of the flesh" and the "salvation of the spirit" in the day of the Lord Jesus. One of our church's confessions, therefore, refers to it as "the last remedy."
Discipline does not, however, just mean excommunication. It involves watchfulness and rebuke on the part of all the members. Matthew 18 teaches that the church as a whole is not even brought into the matter unless the sinner, when confronted with his sin, refuses to repent. We are convinced, then, that there would be little need for formal discipline and exclusion from the church if the members faithfully fulfilled these responsibilities. Would God it were so.

The Way of Christian Discipline (Rev. Ron Hanko)
Because Christian discipline is such a serious thing, careful rules are laid down for it in the Word, especially in Matthew 18. These rules are of the greatest importance.
For one thing, as we have noticed, discipline ordinarily begins with private admonition. When someone has sinned against us or offended us we are required to go to them and point out their sin to them.
Several things need emphasis in that connection. First, it is the sinner himself who must be told, not everyone else. Telling everyone else the sins of others is itself the sin of tale bearing or gossiping and is a deadly evil in the church (Prov. 26:20-26). This is the reason Jesus says in Matthew 18:15, "tell him his sin between thee and him alone."
Secondly, it is the person sinned against who has the primary obligation to go to the one who has sinned (v. 15). All too often in our pride and anger we wait for the person who has sinned to come to us and the result is that we are not reconciled to one another.
Third, rebuking of sin must be done with humility and love. Thus Jesus emphasizes, too, that we are "brothers." Very significant is II Thessalonians 3:15, which tells us that even one who has been excommunicated must still be admonished "as a brother." Too often our failure to gain a brother is due to the way in which we point out his sins ...