The Bible’s own claim is that it represents the complete revelation of God1,2,6,7,9. While there was a time God spoke to man through prophets5,8, that time was replaced by the gospel revelation through His son, Jesus Christ and His time on earth5 and His appointed apostles9.
As of the first century, God’s word had been proclaimed throughout the whole world4,6,8. If the word was sufficiently complete in the first century to save individuals1,3,4,6,8,9, how is it any less complete now and why would it be necessary for God to reveal more? Is the foundation9 really still being laid? (No, of course not!)