How do we know that the mystery of the Gospel is true?

The mystery of the Gospel is confirmed as true through divine revelation. As seen in Romans 16:25-27, it was kept secret since the world began but is now made known through the Scriptures and by the commandment of God. This revelation is not based on human wisdom; rather, it is revealed by the Holy Spirit, as illustrated in John 6:44 and Matthew 16:17. To grasp the mystery of the Gospel, one must be taught by God, resulting in an assurance that this truth comes from a higher, divine source rather than human intellect.