The Spirit itself beareth witness with our spirit, that we are the children of God: Romans 8:16
We are in danger of getting into a bargaining spirit with God when we come to Him— we want the witness of the Spirit before we have done what God tells us to do. If you received the witness of the Spirit before the reality and truth that comes from obedience, it would simply result in sentimental emotion. But when you act on the basis of redemption, and stop the disrespectfulness of debating with God, He immediately gives His witness. As soon as you abandon your own reasoning and arguing, God witnesses to what He has done, and you are amazed at your total disrespect in having kept Him waiting. Adapted from Oswald Chambers, My Utmost for His Highest