The Greek word “asphaleia”

Found only in Lk. 1:4; Acts 5:23; 1 Thess. 5:3, this noun and some related terms “are formed from the alpha-privative and sphallō, which means ‘stumble, fall,’ and by extension ‘fall, be foiled.’ They are particularly common in the literary (Philo, Josephus) and popular (the papyri) Koine” (Spicq, 1:212).

In Acts 5:23 this term describes a “securely locked prison” (Exegetical Dictionary of the New Testament, 1:176). In Lk. 1:4 this word describes “reliability.” Having a false sense of security is the idea in 1 Thess. 5:3.