Peter writes this verse of his epistle to help the reader understand and deal with persecution by knowing their value to and calling by God.
The glory of man is great; we achieve, we love, we give, we develop and we keep on doing so. We can celebrate this as we do the beauty and wonder of the flowers that bloom.
But like those flowers our achievements are temporary; they loose their beauty and wonder. What continues are the leaves and branches of sustained growth, learning and love. It is thus which we must keep nourished whilst rejoicing in our flowers of joy.