What is the mystery of God in the Bible?

In biblical terms, the mystery of God encompasses the hidden truths that can only be understood through divine revelation. This includes the unfolding plan of salvation, as seen through the work of Christ and the gathering of God’s people. Ephesians 1:9 speaks of God making known to us the mystery of His will. It is revealed through the gospel, leading sinners to salvation and conformation to Christ's image, thereby fulfilling God's purpose from eternity past. This involves a relationship where believers are drawn into the knowledge of God's glory.