What's the significance of hyssop in John 19:29? There is just one verse in the New Testament that refers to hyssop and is not referring to the Old Testament:


  John 19:29 (NLT)
  A jar of sour wine was sitting there, so they soaked a sponge in it, put it on a hyssop branch, and held it up to [Jesus'] lips.


Why is the fact that a hyssop branch was used significant enough to mention it by name?
Hyssop represents common faith. Hyssop was a weed that grew practically anywhere. The blood is applied by common faith in God's word.


  EXODUS 12:22 And ye shall take a bunch of hyssop, and dip it in the
  blood that is in the bason, and strike the lintel and the two side
  posts with the blood that is in the bason; and none of you shall go
  out at the door of his house until the morning.


In many of the Old Testament sacrifices (the two turtle doves for the cleansing of the leper, and especially the sacrifice of the red heifer), hyssop was burned in the fire, with the sacrifice, along with scarlet and cedar.


  Numbers 19:6 And the priest shall take cedar wood, and hyssop, and
  scarlet, and cast it into the midst of the burning of the heifer.


Hyssop represents the first step of salvation, believing on the Lord through common faith (justification).

Scarlet represents the blood sacrifice which atones for our sins, and being set aside for service (sanctification).

Cedar represents a Holy God coming to dwell in our hearts (baptism of the Holy Ghost).

The reference to hyssop in John 19:29 ties together the Old Testament prefigure of the red heifer (who died for the sins of the people) with the death of Christ (who died "once for all"). There on Golgotha was Hyssop, the Blood Sacrifice (Scarlet), and Emmanuel (God with Us, Cedar).