“9. Sinomang nagtuturo na mayroong hiwalay at pangwakas na pagaaring-ganap na may bahagi ang katuwiran o kabanalan na mula sa isang Kristiyano (HC 52; BC 37).”
Piper does not hold to any of the Reformed confessions or catechisms. That doesn’t mean he isn’t a Christian or that he doesn’t teach useful things. But it does mean that we shouldn’t be surprised when he teaches something outside the confessional standards.