From An AppealTo The Laymen And Faithful Pastors of the Lutheran Church-Missouri Synod
There is only one reason why Christians must join together to organize congregations, and that is for the express purpose of publicly administering the power of office of the keys. In other words, to publicly forgive sins. Anything else a congregation does doesn't necessarily take a congregation to do. A Christian social club or some other corporate body of Christians will do just fine.
A quick review: "What is the Office of the Keys?It is the unique church power which Christ has given to His Church on earth to forgive the sins of penitent sinners, but not to forgive the sins of the impenitent as long as they do not repent." (A Short Explanation of Dr. Martin Luther's Small Catechism with An American Translation Text.Missourian Publishing Co. Pg. 56)
The power to forgive or not to forgive sins. An absolutely awesome power. And it was given to each of us, miserable sinners all, by Jesus Himself: "'If you forgive sins, they are forgiven; if you don't forgive them, they're not forgiven'" (John 20:23). The power is to be wielded not by "weapons of the flesh" (2 Cor. 10:4), but only by the "sword of the Spirit, which is the Word of God" (Eph. 6:17). The office of the keys, the power to forgive sins, is to be exercised by you and me and all Christians by means of the Word and only the Word - until the end of time.
We have the Word of forgiveness and we've been given instructions for using it. In the first place we are to proclaim it: "Go ye therefore and preach the Gospel to every creature" ( Mark 16:15); "it is the power of God unto salvation to everyone that believeth" ( Rom. 1: 16). Second, we are to baptize: "Go therefore and make disciples of all nations, baptizing them in the name of the father and the Son and of the Holy Spirit" ( Matt. 28:19); "Repent and be baptized everyone of you in the name of Jesus Christ for the remission of sins....." ( Acts 2:38). Third, we are to administer the Lord's Supper: "'Take eat; this is my body which is given for you. Do this in remembrance of me........Drink ye all of you. This cup is the new testament in my blood, which is poured out for many for the forgiveness of sins. Do this as often as you drink of it, in remembrance of me" (Small Catechism.Matt. 26:26-28; Mark 14:22-24; Like 22:19, 20; 1 cor. 11;23-25). Fourth, we are to absolve: "Whosoever sins ye remit, they are remitted to them" (John 20:23).
Note regarding the retaining of sins: "The'keys of the kingdom of heaven'are nothing else, and can be nothing else, than the means of grace, the Gospel. Through the offer of the Gospel, and through nothing else, Christians remit sins and thus open heaven; through withholding the Gospelthey retain sins and thus lock heaven" (Christian Dogmatics.Pieper, III, p. 453. Emphasis added). Another note: Excommunication doesn't fit in at this point notwithstanding widespread belief to the contrary, even, unfortunately, among pastors.
So whenever and wherever the Gospel is proclaimed or the sacraments and absolution are administered, there the authority of office of the keys, the power to forgive sins, is being administered in accordance with the will of God, Father, Son and Holy Spirit.