You live your life. For what purpose?
If you belong to HIM, your purpose is quite simple. He lives in and through you. You are His hands, His feet, His vessel and He fills you with His spirit. You produce fruit which produces seed, through which the tree of life grows and continues and this inner kingdom of heaven (within) expands. It's His purpose, for His pleasure and for His glory- to see LIFE continue, in you.
Imagery is used in scripture to make certain associations. The key understanding of this spiritual (heavenly) kingdom of God is rather 'agricultural.' It's with intent. Jesus taught us repeatedly---- the kingdom of heaven "is like....." and then he gave us examples, but none so stark and simple as that of the seed.
It's a bit like this... You live your life and give it willingly to expand this heavenly kingdom. It's your true purpose. --Like this agave plant. It grows for decades, then rises and in the rising it finally gives it's seed to the wind.... and in dying, it lives on.
Do you see it?