The Bible is fascinating! It’s subtle and provocative and encouraging and challenging and funny and it will exceed our expectations if we let it. The Biblical authors are very clever in the way they write but, unfortunately, we often miss what they are doing just below the surface.
First, they were claiming that Jesus is Lord, therefore, Caesar is not. The phrase “Caesar is Lord” was very common in the ancient Roman world. It was written on coins and pottery, spoken about in poetry and songs; emperor worship was standard all over the empire. So the claim ‘Jesus is Lord’ (and, therefore, Caesar is not) was a politically charged punch in the gut to the Roman Empire, which would have stood out to any ancient person who heard it.
Second, the New Testament authors were claiming that Jesus is Yahweh. Yahweh is God’s personal name (see Exodus 3:14-16). Traditionally the name Yahweh has been translated as LORD (you will notice it in all-caps in your English translations). When the Hebrew Bible (the Old Testament) was translated into Greek (the language of the New Testament), the divine name, Yahweh, was translated using the Greek word Kyrios. This is the same word that the New Testament authors use when they said that Jesus is Lord (kyrios). So to say that Jesus is Lord is to say that Jesus is Yahweh.
Both of these claims give us an appreciation for how provocative it was for the early Christians to claim that Jesus is Lord. Yet in modern western Christianity we can be so comfortable with saying ‘Jesus is Lord’ that we forget the weightiness of that statement.