The kingdom of God, simply put, is all things created that are under submission to God. God created all things in heaven and on earth. The kingdom of God is also called “the kingdom of heaven,” “the kingdom of Christ,” “the kingdom of the Lord,” and “the kingdom.”
On earth, man has free will which allows him to decide whether he will be a part of God’s kingdom or choose to remain outside of it. The angels also had this choice and Satan along with the angels who followed him, chose to rebel against God. As a result, they were cast out of the kingdom.
The Lake of Fire was created for Satan and his angels when they chose to refuse submission to God and it is the eternal home for all those who choose to follow this path. The sad reality is that men who choose not to submit to God will live out eternity there, forever separated from God because of their sin.
Sin is rebellion to God and it is the one thing that forbids entrance into His kingdom. Man lost the right to enter when Adam rebelled against God’s command in the Garden of Eden. But God loved man so much that he provided another way for us to be reconciled to Him so that we may still become a part of His kingdom.
There is only one way and that way is through the blood of Jesus Christ! Because of the sacrifice that Christ made for us on the cross, man has the option to be reconciled to God. Christians are awarded the benefit of receiving the kingdom of God within their hearts when they accept Christ as the Lord of their life and choose to be buried with Him in baptism, after which, they receive the gift of the Holy Spirit and become new creatures in Christ. (See the article titled Baptism: The Work of the Deity (Trinity) for more on this.)
Luke 17:20-21 And when he was demanded of the Pharisees, when the kingdom of God should come, he answered them and said, “The kingdom of God cometh not with observation: 21 Neither shall they say, Lo here! or, lo there! for, behold, the kingdom of God is within you.”
At the end of time, the door of the entrance to the kingdom of God will be closed forever. After Christ’s return, all those who chose submission to God will live out eternity in the kingdom of God and all those who chose rebellion will be cast into the Lake of Fire. Where will you spend eternity? Choose wisely.