The key here is that the axe splits the wood rather than forcefully gets into the wood. Not sure how this is different? Try turning the wood on its side and see

The key here is that the axe splits the wood rather than forcefully gets into the wood. Not sure how this is different? Try turning the wood on its side and see how the axe works then. By striking it parallel to the wood structure, it separates the wood from the point of impact. If one were to strike it orthogonal to the wood structure, this would be pretty pointless.