Why does Napoleon Insist that the windmill must be rebuilt immediately?

The first time when the windmill is destroyed by the storm and blamed on Snowball, or the second time when men from the neighboring farms blow it up. Napoleon insists on immediate action after both instances to prove he is in charge. Snowball needed to be eliminated because there were animals on the farm that still saw him as innocent, and after the windmill was blown up, Napoleon needed those who thought they could destroy them to understand he was not going to lose.