He did not need man’s testimony about man, for he knew what was in a man.
The Messiah do not want men to boost. Many claimed to be followers of Jesus do exactly that. They try to show how great they are, many of them have tittles like «Pastors». They talk about their Church, or their ministry, and all the good things they have done. Jesus rebukes this kind of attitude. The Church is His. And He is the builder, and to Him goes all the honor and glory.