After giving the Torah to the Children of Israel, God emphasizes that they are not to serve idols. He then commands them to serve him on an altar. The altar was used to burn communal sacrifices that were brought daily and on holidays, and for individual sacrifices were brought for repentance or in thanksgiving.
The Talmud explains that before the Tabernacle was constructed, sacrifices were brought on bamot – private altars – and the sacrificial service was performed by the bechorim, the first-born. After the Tabernacle was erected sacrifices could only be brought there and the sacrificial service was performed by the kohanim (priests) – descendants of Aaron.
Serving God on an altar follows the tradition established first by Noah and then the patriarchs, who constructed what were essentially heaps of stones from stones gathered at the location. This was done whenever and wherever there was a theophany, a visible manifestation of God. Since the shechina (divine presence) dwelt in the camp of the Israelites during the Exodus from Egypt and, later, on the Temple Mount in Jerusalem, an altar was necessary.
The Tabernacle actually had two altars; the Altar of Burnt Offering, and the Altar of Incense, also called the Golden altar because it was covered in gold. The Altar of the Burnt Offering was composed of a frame, 5 cubits in length and in breadth, and 3 cubits in height (roughly seven and a half feet on each side by four and a half feet high), made of shittim wood overlaid with brass. Each corner featured a projection, called a “horn” (keranot). The altar was hollow, except for a mesh grate which was placed inside halfway down, on which the wood sat for the burning of the sacrifices. The area under the grate was filled with a mound of earth or stones so it was raised above the rest of the tabernacle. There were rings set on two opposite sides of the altar, through which poles could be placed for carrying it. These poles were also made of shittim wood and covered with brass.
When a person entered through the gate of the tabernacle, the first thing they would see was the brazen altar. Once the fire was kindled in this altar, God ordered that it should never be allowed to die out (Leviticus 6:6).
This was different from the altar in the Temple. The Tabernacle traveled through the desert with the Jews so it was constructed accordingly. The Temple altar did not have poles and was much larger, built entirely of stones with no brass frame. The altar was so large that there was a long ramp leading up to the top.
Between the copper altar and the entrance of the sanctuary stood the laver where the priests would wash their hands and feet. The same section of the Torah in which God commands Israel to build an altar also prohibits the placing of stairs in front of the altar.
The altar, the focal point of the service in the Tabernacle, was made of undressed stone, standing in sharp contrast to the splendor of the ornate gold and silver that decorated the rest of the House of God. The Torah specifies that the stones had to be natural, uncut by any iron tools. The Talmud explains that “iron was created to shorten the life of man, and the altar was created to lengthen the life of man. So it is not fitting that that which shortens should be lifted upon that which lengthens.”
The Midrash teaches that the four letters composing the Hebrew word for altar, mizbeach (מִזְבַּח), are an acronym for mechila (מחילה), forgiveness, zechut (זכות), justification, bracha (ברכה), blessing, and chayim (חיים), life.
The Temple sacrifices remained a central part of the Jews’ service of God throughout history, though the exile made it impossible to continue offering them since, after the consecration of the Temple, Jews were only permitted to bring sacrifices on the Temple Mount.
The Midrash teaches that the altar on Mount Moriah was the same that Noah built, and that Adam had already brought his first sacrifice to this identical spot.
Anyone was able to offer a sacrifice in the Temple, and the other nations took part in this with the Jews acting as intermediaries. In the Third Temple as well, the sacrifices of all, both Jews and non-Jews, will be welcome. The only objections to the sacrifices were expressed by the Essenes whose opposition was directed rather against the illegally appointed high priests than against sacrifices in general.