He did not need man’s testimony about man, for he knew what was in a man.
As the people were wise in trusting in Jesus because of what He did and Who these signs pointed to, so was Jesus wise in not trusting in the people, who would have made Him their earthly king. His knowledge of what was inside people was again an indication of His deity.
Barclay notes that Jesus always wants men to follow Him based on an understanding of the cost and what accepting Him fully means. He never wants men to act upon a moment of emotion because they will later back out when they discover what their decision really means.