The primary difference between insure and ensure is that insure is concerned with the preparation in case something goes wrong or does not go the way you plan or expect it to go, whereas ensure is concerned with the necessary preparation that must be taken in order to make sure that nothing goes wrong, or things go just the way you expect or want them to go. To understand this better, consider the example of a house and fire. You get the house “insured” against fire, which means you will get something like money or other help in case the house does get caught on fire. However, you will “ensure” or make the necessary preparation to make sure that the house does not catch fire.
Insure is commonly used in the commercial sense, whereas ensure is used in a more general sense when talking about giving a guarantee against risk. When a house or car is purchased by a person, he wants to get it insured against risk such as fire or theft, so that in case the car does get stolen or the house get catch fire, the person will be compensated for the loss. Ensure is just a casual or general guarantee that a certain thing will be prevented from happening. The government is often heard saying that they will ensure that the basic rights of every citizen are protected. However, when the basic rights of a citizen are not respected or protected, the government is not liable to pay anything.
In most countries, insure is reserved for financial matters, whereas ensure is used when something is being made certain. The language used in financial matters is often misunderstood by a layman, which is why they end up mixing up words such as insure with ensure.
The pronunciation of insure and ensure is different. Insure begins with an "in" sound, while ensure begins with an "en" or "n" sound.