There are some people who worship Allah on the edge [of faith][6]: if something good comes to them, they are content; but if they are afflicted with a trial, they turn back[7], thus losing both this world and the Hereafter. That is the evident loss.
[6] i.e., with uncertainty, hypocrisy, or heedlessness. [7] lit., they tumble on their faces, i.e., turn back to disbelief.