How do we know that God's way of saving sinners is a mystery?

The way God saves sinners truly is a mystery, as Paul illustrates in Ephesians 3:5. It's revealed by the Spirit and not through human understanding; the natural man cannot grasp the divine workings of salvation. The mystery involves Christ’s righteousness, which is imputed to sinners, highlighting that no one can earn God's favor through works or the law. Instead, salvation is a sovereign act of grace. This understanding assures believers that their salvation is not contingent on their own ability but on God's perfect plan, a plan that has often confounded human wisdom.