Why is the breakdown of a loan repayment into principal and interest of any importance?
It's important because it shows that the amount you owe does not decrease linearly with each payment, and you gain equity as a correspondingly slower rate at the beginning of the loan and faster at the end. This has to be figured in when considering refinancing, or when you sell the place and pay off the mortgage. It also shows why making extra payments toward principal (if your loan permits doing so) is so advantageous -- unlike a normal payment that lowers the whole curve by a notch, reducing the length of time over which interest is due and thus saving you money in the long run. (Modulo possible lost-opportnity costs, of course.)