Surah 22. Al-Hajj, Ayah 11

I.e., wavering between belief and disbelief, and not really committed to either.

Lit., "he turns about on his face" - the "face" (wajh) of man signifying metonymically his whole being.

Lit., "the [most] obvious loss".

 lit., they tumble on their faces.

They are men whose minds are not firm: they will have faith, if all goes well with them, but as soon as they are tried, they are found wanting. They are a different kind from hypocrites. It is not fraud or double dealing that is their sin: it is a weak mind, petty standards of judging right by success, a selfishness that gives nothing but asks for all, a narrow-mindedness that does not go beyond petty mundane calculations-a "nicely calculated less or more" of the good things of this world. They fail in both worlds, and their failure in this world is patent for every on-looker.