Things aren’t so easy anymore. Even though the Israelites had permission of the king, the local leaders were not so happy to see the wall being built. No one likes a fortified city in their midst. They began by making fun of the builders, saying just a fox standing on the wall would tear it down. But then when they saw that the Israelites were determined and continued to build, and it started to take shape, they plotted to stop the work through force.
The Israelites heard about the plot to take them by force and divided up their men where half would work on the walls and half would protect the city. As a result the enemies of the Israelites decided not to attack because they saw that they were prepared. What is that statement, an ounce of prevention is worth a pound of something. This is certainly the case in the case here for sure. Notice the time that they spent to make sure that this was accomplished. They never changed their clothes because they went from building to defending, always having a sword in their hand to be ready.