Charles Ellicott Commentary Zechariah 8:9

"Thus saith Jehovah of hosts: Let your hands be strong, ye that hear in these days these words from the mouth of the prophets that were in the day that the foundation of the house of Jehovah of hosts was laid, even the temple, that it might be built." — Zechariah 8:9 (ASV)

Prophets. —It would almost seem that there were other prophets who spoke at the time besides Haggai and Zechariah.

That the temple might be built. —These words seem to refer to the resumption of the building (Haggai 1:15), when the people diligently set themselves to work.

This contrasts with the first laying of the foundation in the second year of Cyrus, king of Persia, B.C. 537 (Ezra 3:10, compared with Zechariah 1:1). That earlier work could hardly be described as being done "that the temple might be built," since construction was then suspended for about sixteen years.

There is no reason to suppose that the Septuagint read a different preposition before the infinitive "to be built." The Hebrew preposition "to," or rather "with reference to," often denotes "with reference to the time when," i.e., "from the time that" .