Ezekiel 36 prophecies a new kind of cleansing different from the priestly cleansing prescribed by Moses. This new cleansing is directly from God:
25 I will sprinkle clean water on you, and you will be clean; I will cleanse you from all your impurities and from all your idols. 26I will give you a new heart and put a new spirit in you; I will remove from you your heart of stone and give you a heart of flesh. 27And I will put my Spirit in you and move you to follow my decrees and be careful to keep my laws
The Spirit of God will be in you and move you to want to do good. During the time of John the baptizer, the Jews were wondering about the fulfillment of this Ezekiel's prophecy. In addition to John's baptism, in John 3:
22 Jesus and his disciples went out into the Judean countryside, where he spent some time with them, and baptized. 23Now John also was baptizing at Aenon near Salim, because there was plenty of water, and people were coming and being baptized. 24(This was before John was put in prison.) 25An argument developed between some of John’s disciples and a certain Jew [label him J1] over the matter of ceremonial washing.
From the context, J1 was likely to be a disciple of Jesus. They argued about the fulfillment of Ezekiel's prophecy.
26 They came to John and said to him, “Rabbi, that man who was with you on the other side of the Jordan—the one you testified about—look, he is baptizing, and everyone is going to him.”
John’s disciples were jealous of Jesus' disciples. John's reply was both matter-of-fact and gracious.
27 To this John replied, “A person can receive only what is given them from heaven. 28You yourselves can testify that I said, ‘I am not the Messiah but am sent ahead of him.’ 29The bride belongs to the bridegroom. The friend who attends the bridegroom waits and listens for him, and is full of joy when he hears the bridegroom’s voice. That joy is mine, and it is now complete. 30He must become greater; I must become less.”
John was happy to acknowledge the superiority of Jesus. After Jesus' death and resurrection, Paul clarified this superiority in Acts 19:
1 While Apollos was at Corinth, Paul took the road through the interior and arrived at Ephesus. There he found some disciples 2and asked them, “Did you receive the Holy Spirit when you believed?”
They answered, “No, we have not even heard that there is a Holy Spirit.”
3So Paul asked, “Then what baptism did you receive?”
“John’s baptism,” they replied.
4Paul said, “John’s baptism was a baptism of repentance. He told the people to believe in the one coming after him, that is, in Jesus.” 5On hearing this, they were baptized in the name of the Lord Jesus. 6When Paul placed his hands on them, the Holy Spirit came on them, and they spoke in tongues and prophesied.
What is the purpose/significance of John 3:25?
Then there arose a question between some of John’s disciples and the Jews about purifying.
They were arguing about the significance of baptism, the difference between the two baptisms and the Jewish washings, and whether the baptizing and cleansing from sins were to be found with John or with Jesus. It was finally answered clearly by Paul.