Lynda M. from Northern Ireland asks,
I was baptized at the age of 13 before I was really walking with the Lord. It came as a result of covering the topic in a youth Bible class after which we were asked if we would like to be baptized, and considering the majority of the class were doing it, I decided to as well. I recall at the time being too embarrassed to even tell my school friends about it, never mind ask them to come.
The Lord really worked in my life at the age of 20, and that's when I would say he really opened my eyes to what following Jesus was all about. Ideally that's when I would have been baptized, but obviously I already had been. I'd be interested to hear your thoughts on getting baptized for a second time, and if you feel that would be necessary.
We posed the question to Bobby Jamieson, editor at 9Marks and author of the forthcoming book Sound Doctrine: How a Church Grows in the Love and Holiness of God (Crossway). You can also read the paedobaptist answer from Jared Oliphint.
In a nutshell, I'd say yes, you do need to be baptized—for the first time! That's because baptism is for believers, and you seem to be telling me that you were definitely not a Christian when you were "baptized" at 13.
First, know you're not alone. Many Christians have wrestled with this very issue, including a number of members of my own church. And I want to encourage you for taking both baptism and also conversion seriously. That's wonderful evidence of God's grace at work in your life.
Next, here's a super quick sketch of the Bible's teaching on baptism. In Matthew 28:19 Jesus commands his disciples, "Go therefore and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit." So followers of Jesus make disciples, and we baptize those disciples.
This is just what the early Christians did. At the end of his sermon at Pentecost, Peter told the convicted crowd, "Repent and be baptized every one of you in the name of Jesus Christ for the forgiveness of your sins, and you will receive the gift of the Holy Spirit" (Acts 2:38). Then we read that "those who received his word were baptized, and there were added that day about three thousand souls" (Acts 2:41). Note that only those who received the message of the gospel were baptized and added to the church.
What does baptism mean? We read in Romans 6 that we are baptized into Christ's death (Rom. 6:3). We are buried with him in order that we might share in his resurrection life (Rom. 6:4). In other words, baptism is a picture of a believer's union with Christ in his death and resurrection.
In view of all this, I believe, and it sounds like you do too, that baptism is for those—and only those—who have repented of their sin and trusted in Christ for salvation. (Of course, not all Christians agree. For a substantial defense of the believers' baptism position, see here.) Therefore, any "baptism" performed on someone who was not a Christian is simply not baptism by definition.
In other words, you've not been baptized, and you need to be. So I'd strongly encourage you to get baptized---for the first time.
Of course, there's a situation similar to yours in which I wouldn't necessarily encourage someone to be baptized. Let's say you sincerely professed faith in Christ at a young age, and were baptized at 13. But your track record as a Christian was spotty throughout your teenage years, and it's tough to tell in hindsight whether you were genuinely converted at the time you were baptized. If that was your situation, I might encourage you to, as it were, trust the sincerity of your 13-year-old faith. It's easy to mistake childlike faith for no faith at all, and to impose an adult standard of spiritual fruit on a child or even a teenager. In such cases, I'd encourage someone to get baptized only if she came to be absolutely convinced that she was not converted at the time of baptism.
However, I think your situation is much simpler. You didn't get "baptized" as an expression of faith in Christ, but simply to follow the crowd. Your "baptism" was not a public profession of faith in Christ and a public picture of your union with him by faith. Which means it wasn't baptism.
So now you've got the joyful privilege, and responsibility, to obey Jesus' command to be baptized. Don't be ashamed or view this as a do-over. Instead, embrace it as an opportunity to obey God's Word, to give public testimony to the gospel, and to celebrate God's redeeming work in your life.