Final answer:
Penicillin is a powerful drug that has saved many lives, but it is not a cure-all for all illnesses.
Step-by-step explanation:
The main idea of the passage is that while penicillin is a powerful drug that has saved many lives, it is not a cure-all for all illnesses.
Penicillin has been instrumental in saving lives, especially during World War II when it was considered a wonder drug.
However, it is important to recognize that penicillin has limitations and cannot treat all diseases.