How will believers be part of the kingdom when it comes to earth?
Believers are already members of the kingdom, though it presently exists in heaven. When that kingdom comes to earth, they will be part and parcel of it because they are already in it. Having received their resurrected, incorruptible bodies and their reward, they will return to become active participants in the kingdom.
Les teaches that believers today are already members of the kingdom, but the kingdom is not now on earth; it is in heaven. One day that kingdom of heaven will come on the earth, and believers will be part and parcel of it because they are already in it. In Romans 8, those who have the firstfruits of the Spirit groan within themselves waiting for the adoption, the redemption of the body. The soul and spirit are already redeemed, but the body awaits redemption. Paul says in 1 Corinthians 15 that this corruptible body will suddenly become incorruptible when believers go up into the presence of the Lord, receive their reward, and get ready to come back and become active participants in the kingdom. In Colossians 1:12, Paul gives thanks to the Father, who has prepared believers to be partakers of the inheritance.