What security is for
Security is the set of rights a lender holds so it can recover its money from something other than your promise to repay. If the loan runs to plan, the security never comes into play. If it does not, the type of security decides what the lender can do, how quickly, and which of your assets are exposed.
Property lenders rarely rely on a single document. A typical package might pair a mortgage over land with a security interest over a company's other assets and a personal promise from its directors. Knowing what each piece does lets you see the full reach of what you are signing, rather than focusing only on the property named in the offer.