Matthew Poole and continuators on Numbers 5:15

15 Then shall the man bring his wife unto the priest, and he shall bring her offering for her, the tenth part of an Ephah of barley meal, he shall pour no oyl upon it, nor put frankincense thereon ; for it is an offering of jealousie, an offering of memorial, bringing iniquity to remembrance :

She persisting in her denial, and her husband requiring her submission to this way of tryal.

Which was partly because none were to appear before God empty, Exod. 23. 15. partly by way of solemn appeal to God, whom hereby she desired to judge between her and her husband, and partly by way of atonement to appease God, who had for her sins stirred up her husband against her and sent an evil spirit between them. See 1 Sam. 26. 19.

Both because it was a kind of sin-offering, from which these were excluded, Levit. 5. 11. and to testifie her sorrowful sence of the hand of God and of her husbands displeasure, and because she came thither as a delinquent or one suspected of delinquency and under an ill fame and unpleasing both to God and men, as one that wanted that grace and amiableness and joy which oyl signified, and that acceptance with God which frankincense designed, Psal. 141. 2.

Both to God before whom she appeared as a sinner, and to her own conscience, if she were guilty, and, if she were not guilty of this, yet it reminded her of her other sins, for which this might be a punishment.