I have always understood that the “outer darkness” will be a place for the unbelieving. I never heard the teaching that it would be a place where the unfaithful believer would be sent where they would experience the weeping and gnashing of teeth until after the millennium until I was reading a book written by a well known minister and bible teacher. And there is another TV preacher who teaches that those believers who practice the acts of the sinful nature will not inherit the Kingdom based on Galatians 5:16-21. What is the difference between not inheriting the Kingdom and not being in the Kingdom? If you will not inherit the Kingdom, how can you be in it?
Every believer has repeatedly committed one or more of the sins mentioned in Gal 5:16-21. It was not Paul’s intent to condemn all believers who do so. The operative term is “practice the acts of the sinful nature” or as the NIV puts it “live like this”. This implies a lifestyle, not an occasional slip. Paul’s warning that people who maintain this kind of lifestyle won’t inherit the Kingdom was to say that by doing so they identify themselves as unbelievers, because it’s only by the power of the Holy Spirit that we can avoid such a life, and even then the sinful nature can overpower us from time to time. (Gal. 5:17)
That said, there is no Biblical basis for distinguishing between being in the Kingdom and inheriting it. Earlier in the letter to the Galatians Paul wrote,
But when the time had fully come, God sent his Son, born of a woman, born under law, to redeem those under law, that we might receive the full rights of sons. Because we are sons, God sent the Spirit of his Son into our hearts, the Spirit who calls out, “Abba, Father.” So you are no longer a slave, but a son; and since you are a son, God has made you also an heir. (Gal. 4:4-7)
If in chapter 4 He said that God has already made us heirs, how could he say in chapter 5 that some of us will not inherit? That preacher misinterpreted the passage.