Coming to the altar isn't the same as repenting. We may come to the altar and cry, feel guilty for our wicked actions and ask for forgiveness. We would walk away feeling better, but our hearts aren't changed. The Bible sums it up like this...
For godly grief produces a repentance that leads to salvation without regret, whereas worldly grief produces death. - 2 Cor. 7:10
Jesus never gave altar calls, Peter on the day of Pentecost never gave altar call, Paul never tells us to give altar calls. Jesus, Peter, and Paul all did one thing in common, they screamed "Repent and Believe the Gospel". I am not saying you can't do an altar call and repent there, but a simple little prayer must have more to it. Repent means to throw down those things that tangle you. Fighting against sin (Romans 6-7). Putting them to death. When a simple prayer will not do. A drastic change (Ezk. 26:36) must take place (John 3). While I usually don't do altar calls, I may call people to the altar to repent, to walk away with a changed relationship with God and with sin. Charles Spurgeon put it this way when he says come to Christ and not the altar:
'Before you leave this place breathe an earnest prayer to God, saying, 'God be merciful to me a sinner. Lord, I need to be saved. Save me. I call upon Thy name....Lord, I am guilty, I deserve Thy wrath. Lord, I cannot save myself. Lord, I would have a new heart and a right spirit, but what can I do? Lord, I can do nothing, come and work in me to do of Thy good pleasure. Thou alone hast power, I know To save a wretch like me; To whom, or whither should I go If I should run from Thee?
But I now do from my very soul call upon Thy name. Trembling, yet believing, I cast myself wholly upon Thee, O Lord. I trust the blood and righteousness of Thy dear Son.... Lord, save me tonight, for Jesus' sake.' ' 'Go home alone trusting in Jesus. 'I should like to go into the enquiry-room.' I dare say you would, but we are not willing to pander to popular superstition. We fear that in those rooms men are warmed into a fictitious confidence. Very few of the supposed converts of enquiry-rooms turn out well. Go to your God at once, even where you now are. Cast yourself on Christ, at once, ere you stir an inch!'
So with that said, come to Christ and be gripped by the gospel. Do not come to the altar and still walk away with the same stoney heart. Repent, and come to cross and be changed by the washing of his blood!