prostassō

This verb belongs to a family of Greek words built on a base verb meaning "to set in place" (τάσσω), and the prefix aims that setting at somebody. So the picture is not a raised voice but a placement: whoever speaks has the standing to settle the question, and once spoken, the matter is settled.

Across its handful of uses the source of the order is always someone whose word decides the case:

• the angel tells Joseph what to do, and Joseph does exactly that (Matthew 1:24)
• Jesus sends healed men to make the offering the law of Moses laid down (Matthew 8:4, Mark 1:44, Luke 5:14)
• Peter directs a Gentile household to be baptized (Acts 10:48)
• God fixes the periods and the boundaries within which the nations live (Acts 17:26)

That last use shows how far the word reaches. The same verb that reports a spoken instruction can also describe God setting the seasons of history in place, which is why English Bibles say "appointed times" there rather than "commanded times". Nothing shifts inside the verb: an authority has laid something down, and it stands.

Luke 5:14 puts this verb beside another word for giving orders (παραγγέλλω). Jesus first charges the healed man to keep quiet, then sends him to do what Moses had laid down long before. The second verb reaches back to a standing requirement rather than a fresh instruction, and that is the shade this word carries whenever the law is in view.