Simple answer: you can't.
But if the label was instead a field...
so every time i want to display a message as text in a layout i have to insert it in a filed?
A field or a global variable. The field can be a global text field. (Sometimes, you can also set up layout text with conditional formatting so that the text is visible only when specified conditions occur.)
Give us an example of what you want to do and one of us can post a more specific description about how you might get what you want here.