Belonging comes before proving

John does not say we may one day be called children of God. He says we are called that, and then - as if he can hear the objection - he adds, and so we are.
Heiser places this passage among the texts about the believer's status in God's family, and the passage itself holds two tenses at once. Right now: children of God. Not yet: what we will be has not appeared. So the proving is not what makes the belonging true. The belonging is already settled, and the becoming is God's work still in progress.
Scripture links:
- 1 John 3:1 - "See what kind of love the Father has given to us, that we should be called children of God; and so we are."
- 1 John 3:2 - "Beloved, we are God's children now, and what we will be has not yet appeared; but we know that when he appears we shall be like him."
You are not auditioning for the family. You are in it, unfinished.