What position are believers placed in?
Believers are placed in the position of a full-grown son, equal within the family of God. This position comes by adoption, and through it they become joint heirs with Jesus Christ. The context presents this as a status of full sonship, not a lesser relationship, with inheritance rights attached to it.
Les explains that when a person is born into the family of God, they are placed equal as a full-grown son. That position is given by adoption, and the result is that believers become joint heirs with Jesus Christ. He emphasizes not to forget this truth.