Fear of judgement because of unconfessed sin
Acts 5:11 (ASV)
11And great fear came upon the whole church, and upon all that heard these things.
A teacher at Mr. Salee's school confessed his sin before the whole students, opening the door that led the students to confess other sins. By the next day fifty-five students had accepted Christ as their Savior.
Danish missionary, Miss Anna Christiansen, preached on sin, righteousness, and judgement. Her message was used powerfully by the Holy Spirit, and “great fear came upon the while church,” as in Acts 5:11. Many confessed their sins, repented and found the new birth.