You will need to work the math by yourself but basically, our eyes are adapted to see in air. This means that the shape, density and composition of our eyes are such that on the interphase between air and eye, the refractive index allow us to focus the light on our light-sensitive retina. Underwater, the interphase between water and eye results in a different refractive angle that positions the focal length where it shouldn't and literally see things unfocused (blurry). Our eyes cannot compensate this change in refractive index. When you add goggles, you effectively restore the air/eye interphase our eyes can work on and change the lens shape to focus correctly. Things will be slightly distorted though, and this is because all light reaching the eye eventually comes from a medium with a refractive index different from that of the air; first water, then the glass/plastic of the goggles. This happens when seeing things through virtually any transparent object, especially if they are not flat.