The inner golden altar stands as the peak of spiritual service within the Tabernacle. It is dedicated to a single, highly specific purpose, demanding absolute adherence to divine instructions without any human addition or independent initiative. The strict boundaries regarding what can be offered apply exclusively to this inner altar, in direct contrast to the outer copper altar, where various other offerings are not only permitted but form the core of its daily function [מזרחי, שפתי חכמים, גור אריה].
The primary restriction involves the burning of unauthorized or foreign incense. Commentators offer different perspectives on what makes the incense unacceptable, weaving together physical, motivational, and practical concerns. One approach focuses on the physical composition, explaining that any mixture deviating from the exact recipe and measurements commanded by God, or containing extra ingredients, is strictly forbidden [אבן עזרא, רמב״ן, רלב״ג, קאסוטו]. Another perspective examines the motivation behind the offering. While other sacrifices can be brought voluntarily, the incense on this altar must be a mandatory communal obligation. Any private initiative to offer incense, even by a priest, is prohibited, recalling the tragic error of Nadab and Abihu [רש״י, חזקוני, תורה תמימה, מלבי״ם]. A third view looks at the source of the materials, suggesting that ingredients prepared or supplied by outsiders are banned due to concerns that they were not processed with the proper intent for the Commandment [פרדס יוסף].
On a deeper level, these strict rules teach that at the highest peaks of spiritual connection, there is no room for arbitrary choices or personal initiatives. Instead, one must completely align and merge with the will of God [רש״ר הירש]. Consequently, all other types of offerings are entirely banned from this inner space. This includes animal offerings, even a single drop of blood; plant offerings, such as bread, even a tiny handful; and liquid libations like wine or water [רש״י, רבנו בחיי, שטיינזלץ]. The prohibition thoroughly encompasses all these categories [מזרחי, שפתי חכמים]. While other offerings represent partial steps or stages of preparation in serving God, the incense altar embodies absolute perfection, meaning no other forms of service should be mixed into it [רש״ר הירש].
The incense holds a unique status as the most beloved and accepted offering before God. It brings joy and serves as a testament to the complete atonement of the Israelites. In fact, the Divine Presence did not descend into the Tabernacle until the incense was finally burned [רבנו בחיי]. The daily service on this altar was also accompanied by a constant miracle. Although the altar was covered in a layer of gold as thin as a coin, it successfully withstood the intense heat of the burning incense for many generations without the gold ever melting [בכור שור].