What is significant about the mention of the foundation of the temple?
By mentioning the temple foundations, the author of Ezra links Ezra 3:1–6 with Ezra 3:8–13. Laying the foundations is clearly a big and an import stage in the building of the temple.
6 From the first day of the seventh month they began to offer burnt offerings to the LORD. But the foundation of the temple of the LORD was not yet laid.