9 But the height of His glorification had to be preceded by the depth of His passion. Accordingly, He went on to add, “Verily, verily, I say unto you, except a grain of wheat fall into the ground and die, it abides alone; but if it die, it brings forth much fruit.” But He spoke of Himself. He Himself was the grain that had to die, and be multiplied; to suffer death through the unbelief of the Jews, and to be multiplied in the faith of many nations.
Source: Tractates on the Gospel of John (New Advent)