The seed fell into the ground, it germinated, and the life of the original seed disappeared. Here, the word death is used to mean the death of old life. Then the seeds died, the wheat seedlings began to sprout, grow and grow, and then many seeds and many new wheat grains were produced.
Jesus told every Christian not to be afraid of death, because death does not mean the end, but a new beginning. A new beginning also means new blessings and new expansion. One wheat produces many wheat, many wheat, more wheat, ... until countless wheat.