The Woman is Made to Stand Before Yahweh as Prepared For It By the Priest (Numbers 5:18).
‘And the priest shall set the woman before Yahweh, and let the hair of the woman's head go loose, and put the grain offering of memorial in her hands, which is the grain offering of jealousy, and the priest shall have in his hand the water of bitterness which causes the curse.'
It is repeated that the woman was set ‘before Yahweh'. That was the most important part of the process and was repeated so that it might be stamped on the listener's mind when the account was read out. All should know that it was Yahweh Who would judge her, not man.
The woman's hair was then let loose. This symbolically revealed to Yahweh, and more emphatically to those watching, what the charge against the woman was and why she was there. Hair hanging loose was an indication of uncleanness (Leviticus 13:45) and of the fact that she was laid bare before Yahweh. She was being seen by Him as no one ever saw her publicly, with all pretence removed. Then the grain offering of memorial, the reminder to Yahweh of what the woman had done, if she had really done it, was put into her hands. Why the grain was of barley we can only guess. But it was ‘the grain offering of jealousy'. It was the indication to Yahweh of the fact of what her husband feared about her. He thought that she was cheap and low. The thought is possibly also that God was determining whether her faith was a sham. Was her life like barley, of low quality? Like the hair loosed it was the sign of a woman laid bare. If she were innocent it would not be held against her, and Yahweh would not be jealous.
Alternatively the hair loosed might have been seen as taking her back to man's primitive state for her to be judged afresh as man had been judged when accused of sinning in the Garden, with the barley seen as wild grain found in the Garden. It may have been seen as going back to the days before man's increasing sophistication caused the dressing of the hair, to the very beginning. Thus did woman stand once more to be judged by God for possible secret sin as had her ancestress Eve before her.
Or the hair might have been hanging loose in readiness for it to be cut if necessary as a sign of desolation and mourning (Jeremiah 7:29).
The priest then took in his hand ‘the water of bitterness which causes the curse'. It was not yet fully ready for use but the woman and all who were watching would know what it was. That water brought a curse on any guilty person who drank of it. The whole purpose of all this symbolism was to bring home to the woman, if she was guilty, how great her guilt was. She was no longer bringing her purity, or lack of it, before men, she was bringing it before God. (See Zechariah 3:1-3 for a similar idea).