John the Baptist’s forerunner ministry is in all the Gospels – for good reason. You can’t receive the good news without repentance. Matt 3:1 begins with John’s message “Repent for the Kingdom of heaven is near”. He is the one Isaiah prophecied about in Isaiah 40 who would announce a Messianic salvation.
John introduces baptism for Jews – people would have been familiar with it to Gentiles coming into Judaism to wash away Gentile impurities.
The fact he baptised Jews is a big deal
1) Their heritage could not save them
2) It wasn’t self administered – you can’t make your self fit for the kingdom
3) It’s eschatalogical (look to the end) – deliverance from coming wrath.

The struggle for John is that though his baptism dealt with the past it didn’t empower the future. You can sense the frustration in his preaching “Produce fruit in keeping with repentance” .
So John promises the coming of one who will also baptise with the Spirit who is holy – who can empower our future with the power of the Spirit who can make us holy.

Who comes with wind to blow away the chaff and stubble in our lives and fire to burn the chaff away.

Acts 19:2 “Did you receive the Spirit when you believed?”