“Another parable put he forth unto them, saying, The kingdom of Heaven is like to a grain of mustard seed which a man took and sowed in his field, which indeed is the least of all seeds, but when it is grown, it is the greatest among herbs and becomes a tree, so that the birds of the air come and lodge in the branches thereof.” (Matthew 13:31-32)
What is a mystery? A mystery is knowledge that can only be taught by God through direct revelation to an individual. You can hear about mysteries from prophets, books, scripture, other inspired people, but it will never be fully comprehended or internalized without revelation directly to the mind.
Faith of a mustard seed is not totally about how great things can be accomplished by tiny means. It is more about the nature of faith. Yes, great things come about when we exercise a little faith, but there is another mystery being taught here.
The mustard seed has all the information and knowledge that it needs to grow into a large tree. It is embedded in its nature. If given all the resources required it can’t help but grow into a massive tree.
To exercise faith, it is only needful to believe that something that is true is possible. A mustard seed has no capacity to believe or disbelieve it can only react to its environment. Exercising belief for us is the fertile ground and water needed to allow faith to accomplish its purpose. We have within each of us the heavenly DNA to become sons and daughters of a Heavenly Father and Mother. Faith is the means to access that DNA to allow it to unfold and grow.
Exercising faith and practicing belief allows the Holy Spirit to activate the Holy Ghost within each of us. And when we activate the Holy Ghost within us we begin to have access to the treasure house of knowledge, the record of heaven, within us. (Moses 6:61) We then have access to all the nurturing elements, the water, air, and fertile ground we need to grow into the mighty mustard tree. And when become able to support them the birds will come and lodge in our branches. The birds are angels, we will converse and be taught by angels.
The mystery is that it is all there within us. All we have to do is activate our connection with eternity. The Atonement of Christ allows us to do that.