Krishna was a Messenger of God. His Message was the Message of love. He was born in a prison. This was a sign for us to know that all of us are born in the prison of self, the prison of this world. Krishna miraculously escaped from prison. If we try to be good, if we try to be godly, we too can escape from the prison of self.
Krishna, like all the other Manifestations of God, was confronted with the forces of evil. He fought against evil and became victorious. No matter how powerful evil might be, the power of truth is always victorious.
Krishna became the king of Dwarka - which means the small Gate. He was the gate of the knowledge of God Himself. His teachings were for the good of man. But alas! man has rejected them.
Krishna was sad that the people would not understand Him. He complained that people did not believe in Him because He came in human form. They had their own fancies about God and His Manifestation. Therefore, when Krishna claimed that He manifested God, the people rejected Him. This is what Krishna says in the Gita:
"The deluded despise Me clad in human body not knowing MY high nature as Lord of all existence." (Gita, IX, II)
Even His beloved disciple Arjuna could not understand the Divine Power in Krishna. Arjuna could not believe that the temple of man might become the seat of the Divine Being. They say that Krishna had to transfigure Himself into the Divine Form so that Arjuna could see His power and believe in Him. This means that Krishna helped Arjuna to understand His spiritual majesty and grandeur before Arjuna would find faith in the Lord.