NOTES for Exo 30:1-38
Judging by the description given in the Book of Exodus, there were two altars in the Tabernacle: one for sacrifice, the second for incense ("burning"). The burning of incense was a reminder that the sacrifices performed in the courtyard of the Tabernacle (and later in the courtyard of the Temple) are only the external side, a kind of shell, of what takes place in the spiritual world, at that heavenly Throne which, as time went on, was revealed more and more often to the people, finally becoming something inseparable from temple worship as such. No meetings with God in our world would be possible at all if God did not, by His will, dwell in His creation.
He did not simply create the world once and then withdraw, leaving it to its fate. He is constantly present in His world, sustaining its existence by His will. His will touches creation, and the point of this contact, the point of God's meeting with the world, is revealed to us as that Throne which the prophets and hymnographers saw, whose texts we find in the Bible. Later it came to be called the Throne of glory.
If it did not exist, if there were no such point of meeting between God and the world, there would be neither theophanies, nor God's presence as it was revealed to Moses on Sinai and afterward revealed to the people in the Tabernacle and in the Temple, nor sacrifices, which in that case would lose all meaning. Indeed, sacrifices exist as a common meal of God with people, and such a meal is possible only in connection with the revelation of God's presence as it is revealed in the Tabernacle and in the Temple. This means that communion with God as such would turn out to be impossible.
One could then only reflect on God, perhaps try somehow to draw near to Him through contemplative and ascetic practices; yet all this, in essence, would not bring a person closer to God. The abyss separating us from Him is truly and really, not merely in thought, bridgeable only from His side.
The burning of incense and the altar of incense were meant precisely to remind a person that everything happening in the courtyard of the Tabernacle or Temple is only a projection of what happens at the Throne, which a person cannot reach. The main thing - the source and cause of everything that happens at the earthly altar - remains hidden behind the veil, whose symbol becomes the smoke rising upward from the altar of incense. This is an important reminder to everyone who perhaps approached the altar without due reverence.