Unto has 29 separate, but related, definitions in the OED (Oxford English Dictionary). Similar to its close preposition cousin, to, the OED initially states this of unto: “Indicating spatial or local relationship.” What distinguishes unto from to, is the following definition: Expressing or denoting motion directed towards and reaching (a place, point, or goal). Ah, reaching the goal. Delivered.
“For unto us a son is born…” — a son is delivered, a son has personally reached us.
“For to us a son is born…”— a son is directed toward our general proximity.
Which one is more accurate; which one is easier to understand?
Simply put, to gets us in the proximity; but, unto reaches the goal, it reaches the person’s inner man, or enters inside the city walls. Additionally, the words nigh and unto are typically paired together—for unto is closer and more personal than to, as nigh is unobstructedly closer than near. See this example from Acts chapter 8, with commentary in brackets:
“Then the Spirit said unto Philip [directly, reaching to him personally], Go near, and join thyself to this chariot [that would put his position near the chariot, but not necessarily nigh unto the Ethiopian]. And Philip ran thither to him [go in the direction of and ultimately intercept this inanimate chariot]….” (8:29, 30).
After a dialog, with Philip apparently outside the chariot, the Ethiopian invited Philip to come up and sit with him. He desired him to come and get near, or nigh. Their positions changed from Philip being outside the Ethiopian’s ‘personal space’ to Philip being ‘inside.’ The preposition confirms this change:
“Then Philip opened his mouth, and began at the same scripture, and preached unto him Jesus” (8:35).
Notice how the prepositions confirm the near/far relationships of Acts 7:38-40:
“…who received the lively oracles to give unto us [delivered]: To whom [why use the preposition To here? keep reading…] our fathers would not obey, but thrust him from them…”
To was used in order to indicate a distant relationship —they had thrust him away. However, when they approached and spoke directly with Aaron, the preposition changes back to indicate the closer relationship: “Saying unto Aaron…” (7:40).
Part 3 (Jonah) is next.