Note 6 at 1Co 3:15: Paul's whole parable is about Christians. He made that clear in 1Co 3:11 when he revealed that the foundation is Christ. Therefore, when he spoke of those who used the wrong building materials suffering loss, he was not speaking of them being damned. He went on to say here in this verse that they themselves will be saved.

He was describing Christians who lost their rewards because they acted from the flesh (see note 3 at Ro 7:18) instead of the Spirit. Does this mean that there will be some second-class citizens in heaven? No! (See note 6 at Mt 10:42.)