The bronze altar outside the tabernacle was a busy place. The morning and evening sacrifices were presented there, but throughout the day the people came with sacrifices for the priests to offer for them. Exodus 29:42-43 gives you the heart of the purpose of the altar.
You need a substitute. Why bring a sacrifice? Some have suggested that the sacrifice was primarily something going on inside the person bringing it. It helped him feel close to God. This view has been promoted by those who suggest that mankind is inherently good, or at least has a spark of goodness that can be fanned into a flame. Others have suggested that sacrifices really didn’t happen in the wilderness (despite what Exodus says!), but was a practice picked up from the Canaanites, which the prophets later tried to modify in the direction of spiritual worship of God. More recently the idea that God would give his Son to die in the place of sinners has been dismissed as cosmic child abuse.
You need a substitute. The problem with trying to bring yourself near to God is that you are a sinner. Ever since Adam sinned, you and I are not only guilty, our hearts are corrupt, and by nature we don’t want to come. The presence of a holy God does not just make a sinner uncomfortable—it terrifies him. We are objectively guilty before God. For us to come into his presence—and live—the penalty for our sin needs to be paid. His holy wrath against us as sinners needs to be appeased. And that is a basic reason that God had Moses build this altar. Here is where atonement was made for sin. Many of the sacrifices were sin offerings, in which the animal’s life was offered instead of the worshiper’s. Sometimes, in graphic symbolism, the worshiper laid his hand on the animal, picturing the transfer of his guilt to the animal to be sacrificed. The sacrifice was a symbol, but it was also more than that. In the offering God did truly forgive the sins of his people. But there was more to come.
Jesus offered himself as the Lamb of God. That is how John the Baptist announced him. He proclaimed himself to be the Good Shepherd who laid down his life for his sheep. Hebrews keeps sounding the note of how much better Jesus is a High Priest, for he serves, not in an earthly tabernacle, but in the heavenly one. At the heart of the gospel is the substitutionary atonement, the wonderful truth that Christ has died in your place, and both the guilt and the punishment for your sins has been removed. That is the wonderful truth for all who repent of their sins and trust in Jesus. It is impossible to emphasize that too much. And yet there is more.
Meet with your God. Bring your worship and adoration to God. As crucial as the idea of a sacrifice as a substitute is, there is something even deeper. Why was that substitution necessary? What was its purpose? The idea of the sacrifice being a substitute for the sinner and bearing his punishment applied only to animal sacrifices, even then, only to some of them. At God’s command his people also brought grain offering and drink offerings which were poured out before God or burned on the altar. Some of the offerings portrayed the punishment of sin, but some were fellowship offering. The meat of the sacrifice was eaten by the the one bringing the offering, and by the priests. It as a fellowship meal in the presence of God.
Adam and Eve had enjoyed fellowship with God in the Garden—but sin ruptured that relationship. For it to be restored, sin had to be dealt with. Behind the substitutionary atonement lies the purpose of fellowship with God.
Live in fellowship with your God who has come to meet with you. Notice how God describes the tabernacle, with a specific focus on the altar—this is the place of meeting. It is not first of all where the people gather to meet, but it is where God comes to meet with his people. And a holy God can do that only as he first resolves the problem of the guilt and corruption of sin. This is not a bootstrap religion. It is not mankind bringing himself closer to God. Rather, it is God’s work. But he is not satisfied simply with forgiving your sin. He does that with the purpose, the goal, of you having fellowship with him, of you bringing your worship and praise, of you bringing your whole life to him.
“[T]hat which is represented as yielding delight to Jehovah is the surrender of man’s life in consecration of obedience. In this sense, therefore, we must understand the burning upon the altar. . . . Although expiation cannot be made by man himself, and consecration by the grace of God can be subjectively inwrought into the life of man, yet we also know of an active consecratory obedience offered to God on behalf of sinners by Christ. Our Lord employs ritual language, when affirming that He sanctifies Himself for them (i.e., for the suffering of His death) (John 17:19). And Paul does the same, when, speaking of Christ’s active obedience, he says; ‘Christ also loved us, and gave Himself up for us, an offering and a sacrifice to God for an odor of a sweet smell’ (eph. 5:2).” (Geerhardus Vos, Biblical Theology, pp. 186-187).
Look forward to fellowship in the new heavens and earth. Enjoy that fellowship with God today. It is wonderful. It is profound. It means that your growth in your Christian life is important, more important than we often realize. But that fellowship is still marred by sin. Sin corrupts even the best of your worship and service of God. But there is better to come. Hebrews rejoices in the work of the exalted Christ, serving in the heavenly tabernacle, after which the earthly tent was patterned. He is the perfect High Priest. But you have not yet joined him there. You, like Israel, still live in the time called “today” (Hebrews 3 & 4), where you need to be warned against unbelief and pointed to your perfect Savior. You, like Abraham, have your eyes set on a heavenly country, a city whose builder and maker is God (Hebrews 11). You look forward to the new heavens and earth where there is no more sin, no interruption of your worship and service of your God.
Why did God have Moses build the bronze altar? Not only to point you to the perfect sacrifice of his Son, pictured in those many morning and evening sacrifices, but also to show you that he is drawing you, in Christ, to fellowship with him—true fellowship now, and perfect fellowship in the age to come.