Remember Venus on the Half Shell? Those flowers floating around the Goddess are roses.
For a long time, Christians rejected rose symbolism because of their association with Greek and Roman myth. Then finally, in the middle ages, things changed, and the white rose became a symbol of Mary and her virginity. At that same time, the rosary became an important tool for prayer. And where does the word "rosary" come from? From "rose" of course! Perhaps the first rosary was actually a crown or roses or a garland of roses.
In Islam, the rose, which usually flowers on a bush full of thorns, is a symbol of the soul, which may flourish in spite of misery of earthly life.
And don't forget the Rosicrucians. Since the name means "Rosy Cross" the the rose must be a sacred symbol to them.
I'm sure the rose symbolizes many other things, both sacred and profane, but that is enough for now.