There were certain Greeks present at the temple who wanted to see Jesus. These were probably proselytes (Jewish converts) who had come to Jerusalem for the Passover. After Philip and Andrew had informed Him of their desire, He began to disclose that His hour (time of His sacrifice) had come.
Jesus used an allegory of a grain of wheat to explain why He must die. Unless a grain of wheat dies in the ground, it cannot reproduce itself. He could not be glorified unless He died. In a like manner, we cannot live for Christ if we do not die to self. Those who follow and serve Him will be where He is also and be honored by the Father.