There are two baptisms. John preached a baptism of repentance and taught that people must repent from their sin.
The symbol is not necessarily the reality, which is the work of the Spirit of God in conversion. The person who is not really saved ultimately finds the strictness and the separation from the world irksome and odious and unpleasant. Baptism today is a picture of a changed life. The old life is buried as it were in the water, and we rise to newness of life. What a wonderful sign – if you mean it, if it is really is a sign of your conversion. But without conversion, for some even today, it is an empty symbol. Consider a time of awakening and revival. It is very moving and very powerful, and many people come under conviction of sin and repent and turn to Christ. But some get swept into the church by the flood. They think they are converted but they are not. It was a shallow repentance. They wanted something for themselves, and then they became a nuisance to the church, and often become the source of pain and difficulty.
When John the apostle quotes John the Baptist here – ‘I baptize with water’ – he assumes that we are familiar with the rest of John the Baptist’s words in the other gospels. This is why the Greek in John 1:26 puts the emphasis on the ‘I’ and the ‘water’ without completing the contrast. We have to fill in the rest from Matthew 3.11 – but ‘he shall baptize you with the Holy Ghost, and with fire.’