Unfortunately, mortgage lenders don't give their money away for nothing!
As with any loan, they make their profit by charging interest.

This is where mortgages become confusing. Lenders do not just offer
one rate of interest. In fact, they will more than likely offer several at the
same time. What differentiates them, however, are the options
offered and the restrictions imposed.

Take time to consider the different interest rate options open to you.
As always, there are pros and cons to each, meaning that what is
suitable for one person may not be appropriate for another.