When we were born of God we were begotten with the seed of God and that seed in incorruptible. It produces children that have everlasting life. That seed is nothing less than the Word of God. As that word is eternal so is everything that word begets. Peter then compares our existence on this earth to that of a flower.
All flesh is like the grass and the flower.
You plant a seed, a few days later there is a stem and then a flower. Several more days and it dries up and blows away. Man is the same. However, the seed of God produces plants of grace that are a sweet smelling savor to God for all eternity because they will wilt and die. When the Holy Spirit plants the seed of God in the ovum of a sinner's heart there is a new creation.