The use of the English word "terror" in this verse as a translation of the Greek phobos (from which we get our word "phobia") indicates that the frequent Old Testament phrase "fear of the Lord" means much more than implied in the modern euphemism "reverential trust." The only other New Testament use of this phrase is in Acts 9:31: "Then had the churches rest . . . and were edified; and walking in the fear of the Lord, and in the comfort of the Holy Ghost, were multiplied."
These two passages seem to be informing us that when a church is "walking in the terror of the Lord," its members will be seeking every means whereby to "persuade men" to come to Christ, and therefore its numbers will increase.
This impassioned persuasion of the lost is motivated by knowledge that "we must all appear before the judgment seat of Christ" (2 Corinthians 5:10). That is, we know that the Lord Jesus, who died for lost sinners and has commissioned us to tell them of His great salvation, will be highly displeased if we don't do so, or if our testimony is compromised by our selfish lives. At His judgment seat, "the fire shall try every man's work of what sort it is. . . . If any man's work shall be burned, he shall suffer loss: but he himself shall be saved; yet so as by fire" (1 Corinthians 3:13, 15).
The terror of the Lord, when we appear before Him in that day, is not the only motive for witnessing, of course. "The love of Christ constraineth us," and when our testimony is received (our motives being "manifest unto God" and even to the "consciences" of those to whom we witness), then the glorious result is "a new creature" in Christ! (2 Corinthians 5:14, 17). HMM