What does the Bible say about the success of the gospel?

Psalm 78 illustrates that the gospel's success lies in God's sovereignty and faithfulness to His elect. From the time of creation, God designed a gospel that reveals the mystery of salvation through Christ. This success is evidenced by God's continuous calling of His chosen people from generation to generation, ensuring that they hear the gospel and are saved. As seen in Colossians 1, this mystery has been made manifest to the saints, highlighting that salvation is a work of Christ within the hearts of believers.