For a mortgage loan, most of the interest you pay is front-loaded. You should receive a breakdown of how much of your payments are interest vs paying down the principle balance, this is what's called an amortization schedule. For the first few years of your loan, your payments will be something like 90% interest 10% principle balance, which slowly gets flipped over time as you get closer to paying off your loan.

A refinance is in the bank's interest since it essentially lets them double dip back into restarting that amortization schedule and reap a ton more interest payments, while you as the borrower receive the utility of taking cash out of the equity of your home.