Thurisaz is the sound “th”
Anglo-Saxon Rune Poem (from ragweedforge.com)
The thorn is exceedingly sharp,
an evil thing for any knight to touch,uncommonly severe on all who sit among them.
Thurisaz reversed is the expression of a harmful power that is turned around to be protective and guarding. It is not focused on the querent of the reading (such as myself) but instead is keep harmful influences in abeyance. I think for myself part of this extends from the personal work of cleansing that I engaged in today, that by cleaning away any harm that maybe on me, It works to keep it further away from me as well.
I just had another thought about the power of Thurisaz. Part of it’s ability is to penetrate past barriers, either ones that have been constructed, or one that are inhibiting a person. It does this not by overwhelming them, but by finding the weak point, the flaw that when it is struck, bring the rest of the structure with it. This could also be shaped into helping one perceive those key areas, whether for good or ill. If you can perceive your own weakness, you can work to overcome it or transform it. If you can see what composition of the pattern, you can determine how to change the pattern, whether for good or ill, and to know what to do and when to do it to make those changes occur.