"Moses & the Law"
"The bulrush is a lowly, thickly clustered, common plant, growing near the water. Because of these characteristics, it has become a symbol for the multitude of the faithful who lead a humble life and abide by the teaching of the Church, the source of living waters. This explanation found support in Job 8:11, 'Can the rush grow up without mire? Can the flag grow without water?' Also, since the infant Moses ( and Moses is taken as the forerunner of Christ) was found in the bulrushes, they have come to be connected with the place whence salvation came."
In this special setting, the bulrushes symbolize the arrival of Moses who ushered in the Law of the Old Testament.