I read this on the Chabad website
In his Likkutei Torah (Devarim 78d) Rabbi Schneur Zalman of Liadi explains that the altars form the whole heart of the Jew. And corresponding to the two altars of the Sanctuary, the outer and the inner, are the outer and inner levels of the heart, its surface personality and its essential core.
The altar on which the continual fire was to be set was the outer one. And for the Jew this means that the fire of his love for G‑d must be outward, open and revealed. It is not a private possession, to be cherished subconsciously. It must show in the face he sets towards the world.
What I would like to know is from where the Rabbi Schneur Zalman of Liadi got his idea from to compare the altars with the heart. Are there any verses in the Scripture which take this symbolism, or make a alogy or metaphor in similar fashion?
And Secondly, if the continual fire was to be set on the outer one, in order to represent that the fire of his love of G-d must be outward, open and revealed in the surface of one's personality.. then what about the inner altar in which way does it represents the inner essence? Or what about the other continual fire (i.e. light), that of the Ner Tamid that was placed in the inner core?