False assurance
Whether it be an altar call, signing a card or praying a prayer, there is a grave danger in seeking prescribed, non-biblically rooted faith responses. Writing this sort of thing off altogether would be an overreach, but great care is needed by those who would do them. For the all-too-common, cheap manifestations of calls for response have done great damage to the Church and assured many of a saving faith that they do not possess.
The following video will be hard for some to hear. You may be unhappy with Paul Washer's tone, or feel that he should also have talked about how God has at times used “the sinner's prayer” to genuinely save people. But I ask you to put those things aside. For whatever else he could have said, what he does say is important for teachers to hear.
You are not justified by a profession of faith; you are justified by a possession of it. And you cannot manipulate that.
—R.C. Sproul
And yet, we must acknowledge that there is a biblical faith response we do find in the Bible. John Piper explains:
Baptism is the New Testament 'going public' and testifying that you've heard the message, Christ has revealed himself to you as beautiful and attractive and true and worthy. Your heart is drawn out in faith to him. And then, you make it known in some public way. There's nothing wrong with giving altar calls, but the more clear, explicit, biblical way is the way Peter ended his sermon in Acts 2:38. What shall we do, Peter? And Peter said, 'Repent and be baptized—everyone of you—in the name of Jesus.' (full sermon)
A false sense of accomplishment
In like fashion, a call for believers to make a public decision regarding holiness or ministry can give them a sense that they have accomplished something, when really they have just taken the first step.
Consider the call to missions, for example. To become a missionary, certainly one must first come to a point of decision that he/she will “go out for the sake of the Name” (3 John 1:7). But this profession of serving God has no worth in and of itself.
‘What do you think? A man had two sons. And he went to the first and said, “Son, go and work in the vineyard today.” And he answered, “I will not,” but afterward he changed his mind and went. And he went to the other son and said the same. And he answered, “I go, sir,” but did not go. Which of the two did the will of his father?’ [The chief priests and elders] said, "The first." Jesus said to them, ‘Truly, I say to you, the tax collectors and the prostitutes go into the kingdom of God before you.’
—Matthew 21:28-31
Rather, it is the actual going which God deems worthy of reward.
And everyone who has left houses or brothers or sisters or father or mother or children or lands, for my name’s sake, will receive a hundredfold and will inherit eternal life.
—Matthew 19:29
And we should make this distinction clear in our teaching, and in what we publicly acknowledge and celebrate. Standing a man in the front who has just committed to reprioritize his time and begin reading the Bible daily is a much less impressive testimony of grace than publicly acknowledging a person who has just finished reading the entire Bible through for the first time. Making much of a new deacon's ambition to serve in this role means nothing compared to corporately thanking God for a seasoned deacon's years of faithful service. It is the doers of God's word that we want to hold up as examples, not merely those with good intentions.
Likewise, we are not “encouraging” a person by speaking to the great work of God in her life because she has just decided to minister to the homeless. We build up our sister by warning her of the difficulties that lie ahead, offering our help along the way, and reassuring her that God can indeed empower her ministry.