Hyssop is an evergreen, bushy herb growing in arid climates out of rocky soil and out of cracks in ancient walls such as in the old Temple area of Jerusalem. Hyssop was once called a "Holy Herb" because it was used for sprinkling in the cleansing and sacrificial rituals of the Hebrews. Ex 12:22 reads "And you shall take a bunch of hyssop and dip it in the blood that is in the basin, and strike the lintel and the two side posts..." Hyssop, a clean, fresh scent, speaks of spiritual cleansing by the refining fire of the Holy Spirit and the resulting joy and power of being Holy Spirit filled.
PS 51:7. "Purge me with hyssop and I shall be clean; wash me and I shall be whiter than snow."
Acts 1:8. "But you will receive power when the Holy Spirit comes upon you, and you will be My witnesses..."