This saying depends on the understanding that height is part of the natural processes of the world and it cannot be altered or changed. We are the height we are. In a social world that included the vast social differences between rich and poor that existed in Israel (see commentary accompanying 3 Nephi 12:3), a message indicating that worrying cannot change stature (or status) was pragmatic. Although the poor could not think to change height or social class, they could change their relationship to God. (See commentary accompanying verse 25 above.)
Comparison: There is no change from the Matthean text.