The Difference Between the Service of the Outer and Inner Altar

QUESTION: What is the difference between the service of the “outer” Altar and the “inner” Altar?

ANSWER: The service of the “outer” Altar involves elevating the physical to G-d – external aspect of Avodah using garments - קרבן- to draw close; The service of the “inner” Altar involves unifying with G-d through the fire of Ketores and its cloud – internal aspect of Avodah cleaving to G-d with emotions and intellect - קטרת - to bind
(לקוטי שיחות כרך לב, עמ' 98 )