How do we know God's Word is effectual in salvation?

Romans 9 teaches that the effectiveness of God's Word in salvation does not depend on human belief but on God's unchanging purpose. In Isaiah 55:10-11, God assures us that His Word will not return void but will accomplish His intentions, reinforcing the idea that salvation is solely the work of God. The preaching of the gospel serves as the vehicle through which God draws His chosen people to Himself, ensuring that none of His promises fail. This underscores that the glory of salvation belongs entirely to God, who is faithful to His Word.