This may be the greatest question Alma asks of any audience. If you once felt the change of heart, “can ye feel so now?” Alma does not assume that the change of heart is permanent, or that it need only occur once. We can experience the change of heart and then allow that feeling or desire to fade. In Lehi’s dream of the tree of life, there were those who reached the tree and partook of the desirable fruit, and yet still were affected by the world around them (see 1 Nephi 8:25, where it says that they were ashamed).
Therefore, the important question is not whether we have felt the change in the past, but whether we currently feel it, whether we endure to the end.