Well if you're accepting of adaptation look at it this way. The difference in the finches beak is only a small change/adaptation over a small time. Now the environmental changes that forced the adaptation on the finch, will not remain the same forever. The environment will eventually change over time and force the finch to adapt in some small way once again. And if this pattern continues over a large amount of time (with each adaptation adding something new to the finch), you will begin to see a completely different animal compared to what the finch started out as. And there you have it, evolution.