The warnings given to Eckels foreshadowed him a chance to hunt the Tyrannosaurus Rex. However, the Time Safari company couldn't guarantee him a safe return.
The chances of Eckels being killed by a dinosaur or some poisonous animal were really high. Eckels killing any animal could completely alter the whole future.
Also, Eckels might disobey instructions and have to pay a huge penalty to the company.
