The Red Room is a sad memory from Jane’s childhood. It is symbolic of anger and pain. It was Jane’s original prison. When she finds out that Rochester cannot marry her because he is still married to his insane first wife, she feels trapped by social convention and circumstance.
That night I never thought to sleep; but a slumber fell on me as soon as I lay down in bed. I was transported in thought to the scenes of childhood: I dreamed I lay in the red-room at Gateshead; that the night was dark, and my mind impressed with strange fears. The light that long ago had struck me into syncope, recalled in this vision, seemed glidingly to mount the wall, and tremblingly to pause in the center of the obscured ceiling. (enotes etext p. 229)
Jane loves Rochester, and wants with all her heart to marry him, but she can’t. So she is transported back to her childhood fears, where her mother visits her and says “My daughter, flee temptation!” (p. 229) She is reminded of the last time she was trapped and abused, just as she is now metaphorically.