The Kingdom of Heaven is not the Church of Jesus Christ, and it is not “going to Heaven when we die.”
In perhaps the narrowest terms, the Church is the family of Yahweh and the Kingdom is the people who obey Him, whether they are members of His family or not. Identity is only indirectly characterized by work. “Manager” is my work, not my identity. “Son” is my identity, not my job title. You can describe yourself in terms of what you do, but your identity is more truly expressed by your relationships.
John the Baptizer was the greatest prophet that was ever born of a woman, according to Jesus. When faced with the works of the Kingdom being done by Jesus, however, he could not recognize the King. He only knew Jesus as a King because of the revelation he had received as a prophet. He sent word from prison to ask Jesus what was wrong when he couldn’t see Jesus taking up the continuation of John’s ministry of seeing everything through his filter of sin, of right and wrong – good and evil. He was not born of God, so he could not see the Kingdom. Righteousness was out of reach. He could only see sin. Jesus told him to examine His work as manifesting the Kingdom.
To Nicodemus, Jesus answered, “Most assuredly, I say to you, unless one is born of water and the Spirit, he cannot enter the kingdom of God. That which is born of the flesh is flesh, and that which is born of the Spirit is spirit. Do not marvel that I said to you, ‘You must be born again.’ The wind blows where it wishes, and you hear the sound of it, but cannot tell where it comes from and where it goes. So is everyone who is born of the Spirit.” Whoever has been born of God does not sin, for His seed remains in him; and he cannot sin, because he has been born of God. (John 3:5-8; 1 John 3:9)
Having been born of Yahweh, His sons and daughters have His nature in their spirits. That will never change, without regard for their behavior in flesh. To be able to grasp the stark line dividing the unconditional acceptance of sons from the fierce judgement of servants in the Kingdom makes you able to then easily sift through previously unanswered questions about eternal security as sons and being thrust into outer darkness as disobedient sons.
The disobedient virgins were simply outside when the party began. The unclean creatures caught in the dragnet were thrown into the fire. The virgins all had the same nature, therefore were divided based on obedience, and even then, not to destruction. The fish had different natures, therefore they were divided based on their natures, the unclean to destruction (Matthew 25:1-13; Matthew 13:47-50).