How do we know that we are children of God?
Assurance comes by the Spirit Himself bearing witness with our spirit that we are the children of God. Being born ones, we are then heirs of God and joint heirs with Christ, sharing His sufferings and future glory. This positional truth is confirmed internally by the Holy Spirit, not by human effort or merit.
Les explains that every time a child of God is saved, God the Father says He has been waiting for that day and places the believer positionally in a place of full responsibility with God the Son. Though we begin as babes feeding on the milk of the Word, positionally we are right up there with God the Son. The Spirit Himself bears witness with our spirit that we are the children of God. If we are children, born ones, then we are heirs, heirs of God and joint heirs with Christ. What is His is ours, and what is ours should be His. If we suffer with Him, we will also be glorified with Him.
The Spirit itself beareth witness with our spirit, that we are the children of God:
More Questions
Does the Holy Spirit reveal that we are God's children now or only in the future?
The Holy Spirit (better called 'Himself' than 'itself') bears witness with our spirit that we are already—present tense, not future—children of God.
Are believers children of God right now or only in the future?
The Holy Spirit Himself bears witness with our spirit that we are already, in the present tense, children of God, not merely ones who will be children in the future.