Believing in Jesus Christ as the Son of God and Lord of the earth is not a matter of private personal opinion. It is impossible to simply believe in Jesus down in my heart. To believe in Jesus only down in my heart is to disbelieve in the Jesus of the Scriptures.
Faith in the Lord Jesus Christ is a matter of public obedience to divine revelation. If Jesus Christ is not Lord of all then He is not Lord at all. And so, while it is true that you must believe in Jesus Christ down in your heart, that is, sincerely and without reservation, that believing must be a matter of public testimony that Jesus is King.
That is why the first thing we do to declare our loyalty to the promises of God is to receive baptism and to do so publicly. That is why the first thing we do every first day of each new week is to gather publicly before all nations and their rulers, and declare the crown rights of Jesus Christ. We do so openly. We do so inviting all to come and receive the forgiveness we have been given. We do so declaring the Prince of Peace and the only way for all reconciliation to actually occur between men and nations. But we do so uncompromisingly, unapologetically, forcefully, triumphantly, and thankfully.
This is what you have been summoned to do now – by the grace of God and in the power, the saving power for the whole world, of the Holy Spirit. Come and worship our God.