Editor’s note: Clearly this is not a Christian evidence question, but I get versions of this often enough, I feel I should post an answer.
Recently in a Bible study, we were studying John 1. When we came to the issue of the John’s baptism v the baptism of today, we had difficulty. And we have gone back and forth, but I thought I would check in with our “Teacher” to make sure we get this right. In Mark it states that John’s baptism was a “baptism of repentance for the forgiveness of sins” and then it says that Jesus will baptize with or in the Holy Spirit. So there are several disciples a bit stumped on this. Was John’s baptism of repentance for forgiveness of sins able to “save”? If you are forgiven of your sins, then there is no wage of sin (death), so wouldn’t it have saved? Could it have saved without the Holy Spirit? How did John’s baptism differ from the one we do today?
Let me give you the simplest version of an answer I can. I define a “saved” person as one who is “in Christ.” This person has been forgiven of his/her sins and received the indwelling Holy Spirit, which is a “deposit, guaranteeing our inheritance until the redemption of those who are God’s possession” (Eph 1:14). By this definition, those who were baptized with the baptism of John were not “saved.” By this definition, even those baptized by Jesus’ disciples during his ministry were not “saved.” For the young Christian or for the one who does not have a deep knowledge of the Bible, the idea that someone could be forgiven but not saved, may be a bit confusing at first. I believe that David will be in heaven, along with Moses and many Jews, and probably many of those baptized by John. However, they did not have what we have, which is the Holy Spirit as a deposit and guarantee. It is the receiving of the Holy Spirit, hinted at in Jeremiah 31:31f and other places in the Old Testament, but directly referred to by Jesus, which separates “salvation” in Jesus Christ from others who may be with us in heaven, but who did not have the great promises that we have in Christ. Like Jesus said, anyone in the Kingdom of God—anyone in Christ, is greater than John the Baptist, and this is one major reason that we are greater than John the Baptist. We are “in Christ” and have received the Holy Spirit.
Please be aware that this entire statement above is based on the definition I have used for a saved person. Some might use the word “saved” for anyone who has been forgiven of their sins, or anyone who will eventually make it to heaven. I prefer to use precise definitions, and to me the best New Testament definition of a saved person is the one I am using.
I hope this helps. It seems from the way you word your question that this is the direction you were thinking in already.