How do we know the gospel is the basis for judgment?

The basis for judgment according to the gospel is clearly outlined in Romans 2:16, where it states that God will judge the secrets of men by Jesus Christ according to my gospel. This emphasizes that while God's law exposes sin, it is the gospel that reveals God's redemptive plan through Christ. The gospel speaks to both our fallibility as sinners and Christ's sufficiency as our Savior. Therefore, the gospel serves as the standard against which all lives will be evaluated, and only those who have believed in Christ—the fulfillment of that gospel—will stand justly before Him on that day of judgment.