If believers are children of God, what else are they?
Children of God are also heirs—heirs of God and joint heirs with Christ. At the moment of salvation, God declares them full sons of the Father and co-equal with Christ, so everything that belongs to Christ will become theirs. This is the believer's present position.
Les teaches that through the Spirit of Adoption believers are placed as complete heirs with the Father. The Spirit Himself bears witness with our spirit that we are the children of God. And if children, then heirs—heirs of God and joint heirs with Christ. Les emphasizes that the average believer doesn't have a hint of this: at the moment of salvation, when we believed, God declared us a full son of the Father and a joint heir with Christ. He says he can't comprehend it because joint heirship means, like a husband and wife, what's his is hers and vice versa; they are co-equal. That tells him that one day everything that is Christ is going to be ours. He calls it awesome and notes the Book says it, then points to Ephesians 1.