Asphaleia means safety, security, certainty, or firmness — the quality of being without risk of stumbling or falling. From the alpha-privative + sphallō (to cause to stumble, to overthrow). Appearing 3 times in the NT (Luke 1:4; Acts 5:23; 1 Thessalonians 5:3), it encompasses both physical security and intellectual certainty/reliability.
Luke uses asphaleia in his prologue (Luke 1:4) as the epistemic goal of his Gospel: that Theophilus might know the certainty (asphaleian) of the things he had been taught. Scripture's aim is not mere information but sure foundation — unshakeable security for faith. Paul's eschatological use (1 Thessalonians 5:3) is darkly ironic: when people cry "peace and safety [asphaleia]!" — trusting in human security systems — sudden destruction comes. True asphaleia is found only in God, not in human power structures or false prophets promising stability.