Here we have the big picture of the close of this age and the final results of the only two kingdoms there are. Make no mistake, Jesus is telling you that all people will be on one side or the other. There is no neutral ground; it is all a battle ground.
Jesus pictures this as an agricultural battle. We have one field, two farmers, with two types of seeds, and an end time and for all time harvest.
The field of farming is the world. The two farmers are Jesus and the Devil. The seeds of Jesus are the sons of the kingdom of God, those saved by Christ. The seeds of Satan are the sons of his kingdom, the rest of the world. The sowing continues until the time of final revelation.
At the end of this age, Jesus will fully reveal His victory, and His angels will act as the reapers of the harvest. The destiny of the seeds is different (Daniel 12:2). The evil seeds will be sent into eternal destruction along with their father (John 8:44 / Revelation 20:10-15). The good seeds will be sent into eternal glory in the kingdom of their Father (Daniel 12:3 / Revelation 21:1-5).
Jesus says this is no joke; it will go down just like He says (2 Thessalonians 1:5-10).