“The kingdom of heaven is like a mustard seed, which a man took and planted in his field. Though it is the smallest of all seeds, yet when it grows, it is the largest of garden plants and becomes a tree, so that the birds come and perch in its branches.”
Watch historian Tom Holland explain some of the impact that Christianity has had on the West.
An itinerant Jewish preacher of humble origins was healing people and preaching in obscure small towns of Eastern Mediterranean. His message was in essence “Repent, for the kingdom of heaven has come near.” (Matthew 4: 17)
What did he mean by the kingdom of heaven, (or kingdom of God, as he also referred to it)?
“The coming of the kingdom of God is not something that can be observed, nor will people say ‘Here it is’ or ‘There it is’, because the kingdom of God is in your midst.” (Luke 17:20-21)
This blue collar worker , self taught teacher without a pedigree and without powerful friends, was declaring that he was bringing the kingdom of heaven into the world and it would grow to be the largest faith in the world, with evil also finding its way into it (birds often symbolize evil in ancient Jewish thought - see the parable). At the same time he was indicating that the beginning of this process was his dying (the planting of the seed).
The gospel writers could have put the prediction of his own death in his mouth.
But how would the gospel writers have known that this movement - though spreading fast, but still a tiny minority - would grow into the world’s largest faith, with plenty of evil done in its name throughout the centuries? For the first three hundred years - and certainly in the first century - Christians were a persecuted minority everywhere they existed.