And Aaron shall burn thereon sweet incense every morning: when he dresseth the lamps, he shall burn incense upon it. Exodus 30:7 See Exodus 27:21.
Incense had a symbolic significance, as is evident from Ps. 141: 2, “Let my prayer be set forth as incense before Thee.” It became a metaphor for fervent and contrite Prayer. The Rabbis explained that the four letters of the Hebrew word for incense stood for holiness, purity, pity (compassion), and hope—a wonderful summary of the prerequisites of Prayer and of its spiritual results in the lives of men.
(Hertz, Dr. J.H., The Pentateuch and Haftorahs, 2nd Ed., Soncino Press, London, 1992, pg 339)