Generally speaking, whispering is not considered very good for your voice. Because your vocal folds are held stiffly together, loud whispering can dry out the vocal folds very quickly. So you don’t want to whisper for long periods, and certainly not if you’ve injured your voice: that’s just going to make matters worse.
But as a private exercise, something to do for yourself, a little whispering won’t kill you. Of course, you’re going to want to be well hydrated, so have your water bottle handy.
The point of this exercise is to find a personal, intimate connection to a text. This is, perhaps, similar in intention to the Hand Touch Exercise, in that the hope is that whispering the text will help you connect to the language more strongly. For some, I might recommend that they do this exercise first with their eyes closed in an attempt to internalize the speaking process as much as possible. Then, on a second pass through the text, or in the second half of a text, once a strong, personal connection has been established, open the eyes and connect with someone in the space (or, at very worst, an object that you can talk at.)
It’s really important that you don’t try to be heard by anyone. This is for you. Feel the substance of the language, the pop and crunch of the plosives and affricates, the shush of the fricatives, the hiss of sibilants. Try to open your throat wide so that the vowels are even more silent. With your throat wide open, you’ll be “spending” more breath than normal, so you may need to breathe a bit more often than you would when you speak the text aloud, but keep thinking this is small, and quiet and personal.
Once you’ve been through the text once or twice on a very quiet personal whisper, you should speak the text, again quietly, on voice. Try not to lose the sensitivity to the texture of the consonants within the text, the personal connection to the language, but gently turn the language out, from your inner self, to yourself in the world. Affect a partner, make them change, get them to think or act differently, to see the world as you see it.
A whisper may not be strong like a shout, but it has a power to bring us to attention, to focus, and draw us to our personal centre. Next time you need to connect with a text on a deeper level, try a whisper.