There are debates in seminary coffee shops as to whether evangelism belongs in the corporate worship service of the local church. The argument goes something like this: the church should gather to worship and be taught the Bible, and then the believers should go about doing the business of living for Christ and evangelizing friends, neighbors, relatives, etc. Therefore, public calls to salvation (with or without an invitation) are unnecessary.
Now, up until that last sentence, I'm okay. I'm okay with believers gathering to worship God, to study the Bible, and then to go about their lives as missionaries for the Lord Jesus Christ. The idea, though, that we should not compel people to trust Christ in a local church service is unthinkable. There are two primary reasons why I think this: a biblical reason and a practical reason.
First, the biblical reason is that it follows the example of Paul. In writing 2 Corinthians, Paul is clearly writing to the church...he says so in his opening sentence. These are supposed to be men and women who believe in the Lord Jesus Christ. He speaks words of correction, instruction, and encouragement to the church. In fact, Paul is trying to re-establish a trusting "apostle-church" relationship with them by defending his ministry. He comes to the end of chapter 5, and he proceeds to get into matters of the Gospel, specifically that the death of Christ made it possible for men and women to be reconciled to God. After all, prior to conversion, we are all enemies of Christ (Romans 5:10; Philippians 3:18; Colossians 1:21). What interests me is verse 20 of chapter 5. Paul says "Be reconciled to God." He is talking to the church, he is talking about the offer of salvation that has been made by God through Jesus Christ, and he tells the recipients of the letter: be reconciled to God. Paul must have known that 2 Corinthians 6:1 had been true in some of their lives...that they received "God's grace in vain."
Second, the practical reason is this...I think we are living in a day when there are many "churches of Corinth." God's grace is received in vain all the time...from the man who prayed a prayer and was baptized, only to ignore any call to discipleship after that...to the teenager who has been in the church every time the doors are open, has prayed a prayer and been baptized, has good friends in the church, but when it comes to real, personal faith, it's not really there. These are fictional people that represent much of the current church landscape. God's grace is received in vain all the time. So, what is our duty as the church? What are we to do? Preach and teach the Word, always pointing our audience to Christ, and calling anyone who hears to repent and believe, so that they might be saved.
There is certainly a need for "Bob and Sally Christian" to be evangelists in their everyday lives, but there is an equal need to evangelize the pew potato who thinks everything is okay when it might not be.