Hyssop, אזוב, is used several times in the Torah in purification processes. See for example Shemos 12:22, where Moshe Rabbeinu summoned all the elders of Israel and told them:
Take a bunch of hyssop, dip it in the blood that is in the basin, and apply some of the blood that is in the basin to the lintel and to the two doorposts.
Concerning a metzora, e.g. a leper, the purification process also involves hyssop, as told in Vayikra 14:4-6:
the priest shall order two live pure birds, cedar wood, crimson stuff, and hyssop to be brought for the one to be purified [...] and he shall take the live bird, along with the cedar wood, the crimson stuff, and the hyssop, and dip them together with the live bird in the blood of the bird that was slaughtered over the fresh water.
Rashi tells us:
אזוב HYSSOP — a kind of herb which has thin stalks.
The Toldos Yitzchok, in his commentary on Vayikra 14:4 explains the reason why the Torah commands to take cedar wood and hyssop. Cedar wood is from a big tree, hyssop is small (my own interpretation of this Toldos Yitzchok).
Dovid HaMelech in Tehillim 51:9 also refers to hyssop:
Purge me with hyssop till I am pure
Why was hyssop used in some purification processes, does hyssop represent something deeper?
I am looking for an explanation from mefarshim, contemporary very welcome!