This is a mysterious metaphor of how God acts on Earth now and in the future.
It seems to start small like a mustard seed but it will eventually grow to overshadow all else.
The kingdom of God will yield fruit according to God’s plan.
The kingdom is not only in the future but is also unfolding now.
We are included in the kingdom. We are, indeed, challenged to support its spread.
Are we watching and praying for guidance?
Readings: https://bible.usccb.org/bible/readings/061321.cfm