Ex. 27:1–2 – And make the altar of acacia wood, five cubits square and three cubits high [within reach of all]. Make horns for it on its four corners; they shall be of one piece with it, and you shall overlay it with bronze.
The altar simply represents the Cross. It was the only place sacrifices could be offered and God made sure to specify every detail of its design. God chose the location of the altar, what was to be sacrificed there, the material it was made out of, and the size of it. Like the rest of the Tabernacle, everything making the altar also had symbolism in the Kingdom of God.
The wood is humanity, reminding us that Christ became man to experience our pain, as well as to give his life in exchange for ours. The length and width, which makes a square, typifies that the grace of God is available for all of mankind. The horns on all corners represent the Blood of Christ, which is also available to all of mankind. The height, three cubits, even symbolizes the Trinity.
At the Cross, God rendered final judgment on sin. With the Altar, the Brass that makes the Altar Brazen defines this judgement. The grate on the Altar is also made of brass, with no wood, so it can withstand the intense heat of the fire, both the physical fire, and God’s fire.
The Altar is clearly important to God, and it should be equally be important to us, reminding of the ultimate sacrifice foretold by God in the Altar’s creation and existence.