If you are reading a modern translation, you will find this is translated rather differently – knowing therefore the fear of the Lord. The word fear is substituted for terror.
It is because we know the terror of the Lord that churches should have an evangelistic service every Sunday where they focus on persuasive, reasoning preaching, persuading people of the need of salvation and the work of Christ. We should not just wave the flag and say, ‘You are a sinner, Christ is a Saviour, you need a Saviour, come to him.’ We go to all the arguments of the Scripture. ‘This is what you lose; this is what you gain; this is why you need redemption.’ We persuade, we appeal. But that is gone in the more modern translations and the study Bibles. They just want Paul to be justifying his defending of himself.