What does John 3:26 mean?
Based on what we read in verse 25, this statement may have been coming from "the Jews," which is John's general term for the local religious leaders. The intent may have been to start a rivalry between the followers of Jesus, and those of John the Baptist. This was prior to the arrest and execution of the Baptist. During that time, the area around Jerusalem was filled with the preaching of both John the Baptist and Jesus. And, according to verse 23, there was a considerable response. This comment may have been an attempt to inspire competition between the two men. The local leaders may have assumed that the Baptist would become jealous. Then, he and Jesus would waste time and energy fighting each other.The other possibility is that a single leader, probably Nicodemus, spoke to followers of the Baptist. They, in turn, went to the Baptist to complain about Jesus gaining more followers.
Either way, this is a common strategy used by the Devil. Instead of focusing on God's glory, we seek our own. John the Baptist doesn't fall for the trap. He's already content with what God has given him. In fact, he's happy to see that Jesus is gaining followers, according to the next few verses. That's what his mission was.