Scripture: Therefore I am informing you that no one speaking by God’s Spirit says, “A curse be upon Jesus,” and no one can say, “Jesus is Lord,” except by the Holy Spirit. – 1 Corinthians 12:3
To call Jesus “Lord” is to confess to be His servant and to seek His honor alone, to act as His witness by bearing His Word before all. In this text, Paul is referring to the office which represents Christ and bears His Word. So, when the office fulfills these conditions and points others to Christ as Lord, it is truly the message of the Holy Spirit, even though the person who fills the office not directly possess the Holy Spirit. It is the office itself, created by the Spirit which is of the Spirit.
In this office, there is simply no room for false teaching or cunning invention of personal, opinion-driven theology. He who fills this office must be sincere if he is to be a minister of Christ, an apostle, or one who handles the Word of God. And only the Holy Spirit can offer him such assurance.
All Christians may (and should) call Christ “Lord.” It is only by the Holy Spirit that anyone could call Him “Lord” and by this every Christian can be assured he serves Christ. When giving a sermon, or when listening to a sermon, when baptizing a child, or bringing a child to baptism, when carrying out your daily duties, or assigning those duties, simply ask yourself: Are you doing these things from faith, driven by the Spirit, without any misgivings or hypocritical pursuits, or mechanically, and can you boast — even if it means death — that you serve and seek to please Christ in these things? This is what it is to call Christ, “Lord.” Keep in mind that the flesh is weak and the heart doubts over this, which is why you must not trust your flesh, feelings, or give into your fears. Instead, you need the Holy Spirit to guide and comfort you so that should you fall, you will be restored.
We may all be somewhat terrified at this, especially as we consider our sins and weaknesses. Even so, we must learn to say of Christ Jesus: “You are my Lord, and I am Your servant. I believe in You, I trust Your Word, and seek to be with You and all the faithful and to possess You by Word and Sacrament.” Otherwise, on the Last Day, Christ will surely not acknowledge us.