“Let both grow together until the harvest, and at harvest time I will tell the reapers, ‘Gather the weeds first and bind them in bundles to be burned, but gather the wheat into my barn.’” (Matthew 13:30)
Basically, it’s totally clear who belongs to God’s Kingdom and who does not. Everyone who believes in Jesus Christ as his Lord and Savior inherits His Kingdom. Everyone who rejects Him and does not believe in Him makes himself an outsider. But we can’t always tell from the outside who is a citizen of God’s Kingdom and who is not. Some people are like “ravenous wolves in sheep’s clothing” who present themselves as Christians with the aim of destroying the church or of somehow profiting from their position as respected church members. This is a real danger, and we should be alert to people who bring false teachings into the church or whose life does not correspond to Jesus’ commandments, thereby showing that their faith is not real. But it’s not our task to judge who is a child of God and who is not.
In Matthew 13, Jesus tells a parable about a field where wheat and weeds grow up together, but are separated at the harvest. In the same way, Jesus will judge every single human; His children may enter the joy of their King, while non-believers are cast out. Jesus knows every human’s heart, He will judge them fairly.