The last paragraph shows Frederic’s pessimistic view of life. He sees no way to escape death! In this passage the ants symbolize mankind. They are running up and down the log without any orientation, just like most people do in life until they die!
To put this on a religious level, one could say that Frederic is an atheist. He could have been the saviour, the Lord for the ants by just pulling them out of the fire. But since he believes there is no God, he just pours a cup of water on the ants and leaves them to the fire.
In this last passage the author supports the idea that there is no way of escaping from certain death.

Ernesto Kettner