3:12-15 To what is Paul referring here?

Paul is referring here to the Judgement Seat of Christ where Christ will evaluate the earthly ministry of every Christian. Gold, silver and precious stones, which can withstand the refining fire symbolise works that endure to God's glory.

Wood, hay and stubble represent works having no eternal value. They have not endured to God's glory and thus cannot withstand the refining fire, but Christians will not lose their salvation when this happens because the Judgement Seat of Christ is for all those who go to heaven. It is not to determine our eternal destination but our position in heaven.

It is for rewards or loss of them, not salvation (CP Job 23:10; Zech 13:8-9; and Mal 3:1-3 with Ro 14:10-12; 1Cor 4:4-5 and Rev 3:18). See also comments on Ro 14:10-12; 1Cor 4:2-5 and 2Ti 1:12, and author's study Coming Judgements of God in his book Advanced Studies in the Christian Faith (Volume 1).