What did Zacharias understand about the prophetic plan?
Zacharias understood that once his son announced the coming king, the king would come and Israel would receive her kingdom. This fulfilled the Old Testament prophetic program and God's covenant oath to Abraham, promising mercy to the fathers and salvation from Israel's enemies. It was confined to the house of David and did not include Gentiles.
Les explains that Zacharias understood the prophetic plan: once his little son announced the coming of the king, the king would come, and Israel would have her kingdom. Zacharias spoke of a horn of salvation raised up in the house of his servant David, a promise confined to Israel and not including the Gentiles. This was according to what God spoke by the mouth of all His holy prophets, the Old Testament prophetic program. The promised salvation was not from sins but from enemies—the Romans and all who hated Israel. It was to perform the mercy promised to the fathers and to remember His holy covenant, the oath sworn to Abraham. Les points out that Matthew 1 and Luke 1 both go back to Abraham, and everything Jesus does in His earthly ministry is based on that covenant.