that they try sort it out between themselves and as selflessly as possible

it is the ruling of God over all creation which is human, animals and beasts. Because God gave the earth to human beings, a time will come whereby His son will inherit all that His Father has. He (Son) will rule over heaven and earth.

As the Son says in Mark 1:15. "The time is fulfilled, and the kingdom of God has come near; repent, and believe in the good news." He is telling us to repent of all our sins and do right because when the time is near, all those who do bad will not see the kingdom of God; they will be thrown into the fire. But those who do good will be given the crown of eternal life, and will see the kingdom of God.