The Kingdom of Heaven is a term preferred by Matthew in his gospel. Scholars believe this is a cultural sensitivity to the Jewish people who reverenced the name of God so much they would not speak it or write it, but used other synonyms. Even so, Matthew quotes Jesus using both phrases to demonstrate their equivalence (Matt. 19:23-24). So we can see that God’s kingdom is of heaven, but in Jesus and through his ministry God’s kingdom is becoming manifest on the earth. To illustrate this, Jesus told a story of how God’s kingdom is like the planting of a tiny seed that grows (initially in secret) and becomes something far greater that changes the environment around it, creating blessing and benefit where it flourishes.
Matthew 13:31-32 (NKJV)
Another parable He put forth to them, saying: “The kingdom of heaven is like a mustard seed, which a man took and sowed in his field, which indeed is the least of all the seeds; but when it is grown it is greater than the herbs and becomes a tree, so that the birds of the air come and nest in its branches.”