Jesus asked, "What is the kingdom of God like? What can I compare it to? It's like a mustard seed that someone planted in a garden. It grew and became a tree, and the birds nested in its branches." He asked again, "What can I compare the kingdom of God to? It's like yeast that a woman mixed into a large amount of flour until the yeast worked its way through all the dough." Luke 13:18-21, God's Word Translation
Sometimes the Lord's parables are a little confusing, and on this one, I'm just giving you my opinion. If the Lord later explained it to His followers, it isn't mentioned in Luke. I'm not a theologian, either, just a simple Christian struggling to understand and carry out God's plan for me.
The mustard seed is the smallest seed the Jewish farmers would have planted, yet it grew into a plant sometimes ten feet tall.
Yeast is an amazing substance. Have you ever made bread or watched it being made? I used to bake bread for the family when my children were all at home. I made six large (eighteen-inch) loaves at a time. I mixed this little packet of yeast--about a tablespoon full--into a large bowl with about 10 cups of flour with a little sugar, and milk, and water. The yeast makes this dough more than double in size. It would work with much larger amounts of dough, too.
In other words, it takes a seed a while, but it can make a very large plan. Yeast works faster, but a small amount can make a lot of bread.
Are you seeing a parallel here? The kingdom of God will grow. All we have to do is speak out for God. If we keep silent, who will go for Him?
Prayer: Lord God, please help me to plant Your word so Your kingdom will grow to fill this entire world! For Your Son's sake and for Your everlasting kingdom, amen.