God says the fire will try our work, our life, the harvest of our time on Earth, to see what sort it is. (1Co 3:13) If anything of our life abides the fire, we receive eternal reward (1Co 3:14); otherwise we suffer eternal loss. (1Co 3:15)
Fire is evidently a reference to Judgment Day (2Pe 3:7), when everyone shall give account of himself to God. (Ro 14:12) The concept of sort, or type, evidently refers to whether our work is essentially good or evil; it also indicates degree: how good or evil.
Since we’re made in God’s image, we intuitively understand the concept of good and evil: it’s in our DNA. God has defined it for us, but we tend to reject God’s view and make up our own as we go, even disagreeing among ourselves. But God doesn’t change (Ja 1:17), and justice demands that He use His own definition. He will.
So, what’s God’s criteria here? What’s He looking for? What makes something we do, or who we are, good or evil? What is success? What is failure?
Understanding this, is to understand everything that’s really worth understanding; to miss this, is to miss, well, everything. (Mk 8:36) Most of us will get this wrong (Mt 7:22-23), and only because we don’t want to get it right.
It’s not our actions in themselves that make us good or evil, but why we do what we do (1Co 13:3), and there are ultimately only two possibilities: we’re either out to please ourselves, or God. (Php 2:21) Living merely to please ourselves, self-orientation, is the essence of all rebellion. (Ps 2:3) Each life will be characterized primarily by one motive or the other, love or selfishness, but not both. (Mt 12:33)
In being overly concerned with Man’s approval we’re driven by fear of his displeasure (Jn 12:43), and this is sin (1Co 7:23), selfish and evil by definition. (Ja 4:17) We can’t be the servants of Christ if we’re slaves to fear (Ga 1:10); fear ensnares us, polluting our motives and service. (Pr 29:25)
God will inspect every activity of our lives, testing it against holiness, and expose our every motive, which will reveal our general life’s orientation, to the universe. His fire will burn up everything that isn’t rooted in Christ (Jn 15:6), in the pleasure of God. (Re 4:11) Everything He hasn’t planted will be rooted up. (Mt 15:13)