Sometimes it is helpful to have visuals to appreciate the message and content of a book like Leviticus. Here are two I've found helpful. One is from Chuck Swindoll, the pastor of Stonebriar Community Church. The other is by the Bible Project. Do you notice the wonderful thematic symmetry of Leviticus?

"It is most holy of the offerings to the Lord made by fire" (Leviticus 2:3).

Why is the grain offering considered most holy where the other offerings are not. See th explanation by Keil and Delitzsch:

“The term ‘most holy’ is applied to all the sacrificial gifts that were consecrated to Jehovah, in this sense, that such portions as were not burned upon the altar were to be eaten by the priests alone in a holy place; the laity, and even such of the Levites as were not priests, being prohibited from partaking of them … in fact all the holy sacrificial gifts, in which there was any fear lest a portion should be perverted to other objects,—were called most holy; whereas the burnt-offerings, the priestly meal-offerings (chap. vi. 12-16) and other sacrifices, which were quite as holy, were not called most holy, because the command to burn them entirely precluded the possibility of their being devoted to any of the ordinary purposes of life.” C. F. Keil and F. Delitzsch, Biblical Commentary on the Old Testament, trans. by James Martin (Grand Rapids: Wm. B. Eerdmans Publishing Company, 1968 [reprint]), II, p. 293.

Notice the following verses, which establish the regulations for sacrificial atonement for sins by the whole assembly, the leader, and the common person. One thing that should jump out at you is that these regulations are all for atonement for uninentional sins. In other words, there is NO sacrificial atonement for intentional sins.

General rule for Unintentional sins

Then the Lord spoke to Moses, saying, “Speak to the sons of Israel, saying, ‘If a person sins unintentionally in any of the things which the Lord has commanded not to be done, and commits any of them, if the anointed priest sins so as to bring guilt on the people, then let him offer to the Lord a bull without defect as a sin offering for the sin he has committed (Leviticus 4:1-3).

Unintentional sin by Whole Assembly of Israel

‘Now if the whole congregation of Israel commits error and the matter escapes the notice of the assembly, and they commit any of the things which the Lord has commanded not to be done, and they become guilty; when the sin which they have committed becomes known, then the assembly shall offer a bull of the herd for a sin offering and bring it before the tent of meeting.... So the priest shall make atonement for them, and they will be forgiven (Leviticus 4:13-14,20).

 Unintentional sin by Leaders

‘When a leader sins and unintentionally does any one of all the things which the Lord his God has commanded not to be done, and he becomes guilty, if his sin which he has committed is made known to him, he shall bring for his offering a goat, a male without defect... Thus the priest shall make atonement for him in regard to his sin, and he will be forgiven (Leviticus 4:22-23,26).

 Unintentional sin by a Common Person

Now if anyone of the common people sins unintentionally in doing any of the things which the Lord has commanded not to be done, and becomes guilty, if his sin which he has committed is made known to him, then he shall bring for his offering a goat, a female without defect, for his sin which he has committed... Thus the priest shall make atonement for him, and he will be forgiven (Leviticus 4:27-28,31).

Intentional sins fall into the realm of either God's just punishment or His sovereign grace. Even though in the twentieth century, we often do not consider accidental wrongs as wrongs at all, the Bible considers all wrongs, accidental or otherwise, with or without knowledge, well-intended or otherwise, as sin and attaches guilt. However, the sacrificial system was developed for the purpose of providing atonement for these kinds of sins. But there was no sacrifice or burnt offering for intentional sins. This is why David ought to have received the death penalty for his adultery with Bathsheba and for his murderous plot against Uriah, her husband. Yet, God sovereignly chose to forgive his sin and preserve his life:

Nathan replied, “The Lord has taken away your sin. You are not going to die (2 Samuel 12:13).

David realized that he could not perform enough sacrifices or burnt offerings to atone for his sins, so his only appeal was to humble himself and surrender to God's grace:

For I know my transgressions,
and my sin is always before me.
Against you, you only, have I sinned
and done what is evil in your sight;
so you are right in your verdict
and justified when you judge (Psalm 51:3-4).

You do not delight in sacrifice, or I would bring it;
you do not take pleasure in burnt offerings.
My sacrifice, O God, is a broken spirit;
a broken and contrite heart
you, God, will not despise (Psalm 51:16-17).

This is our only appeal to God as well. We are all deserving of God's wrathful judgment, but we humble ourselves, acknowledge our sin, and submit to God's sovereign verdict. As the Bible teaches in John 3:19,

This is the verdict: Light has come into the world, but people loved darkness instead of light because their deeds were evil.

Such is the attitude and fate of every human being in the world. We reject God's Light. However, there are some who live by the truth and come into the light. How can this be? God makes it so by His grace. This is why we also read in John 3:21,

But he who practices the truth comes to the Light, so that his deeds may be manifested as having been wrought in God."

Every true believer ought to have this same confession. If I come to the light, if I practice the truth, it is not I but God, who has done it.

I am so glad we are no longer bound to these rituals. For every sin, there is a different offering that must be made. Apparently, God really likes BBQ. The burnt offering has to be freely offered, unless the burnt offering is in response to a sin. And even then, it is a ritual as described here.

We were given the law so we could see how futile it was to try to live by the law.  The Israelites were given this priesthood and ritual sacrifices so that they would eventually see how futile it is to sin and ritually atone. Their sacrifices had to be made freely in front of the Lord or it was a worthless action. Unfortunately, that is what it became. It did not impact their ultimate actions. The cost to the Hebrew people wasn't personal. They could go ahead and sin, and all they had to do was go to the priest, slaughter an animal, and voila! Their conscience was clear. As a nation, they could sin and voila! Slaughter an animal, and all was good, the relationship was restored by the blood substitute....  

 Christ came to make it personal; so that we could realize how devastating sin is, and how the consequences can be life and multi-generational altering; that's why he came. Instead of empty ritual, I have been restored to full relationship with Christ! That is the beauty of these passages...

Yujin responds... An important thing to remember is that animal sacrifices only covered unintentional sins. In other words, sins done intentionally required restitution or else, if a capital sin, the death penalty (e.g. Leviticus 5:14-19; Numbers 35:16-34; Deuteronomy 19:16-21).

Lay your hand on the animal’s head, and the LORD will accept its death in your place to purify you (Leviticus 1:4).

"Leviticus" is named after the priestly tribe of Levites, one of the twelve sons of Jacob. Later we discover that the Levites were those chosen to replace the first-born sons of Israel, who had to be redeemed from the LORD, who had preserved their lives in the tenth plague in Egypt (Numbers 3:11-13). Now, there were not enough Levites to cover all the firstborn males in Israel, therefore, the remainder of these firstborn of Israel had to be redeemed with money (Numbers 3:46-48). 

However, we should not make too much of the name "Leviticus" because it was not given by God. It was added later by men to identify the book among the other books of the Bible. Nevertheless, much of the book is about the Levites, who were priests to God.

A key concept from Leviticus has to do with substiutionary atonement, which is especially explained in Leviticus 16. This concept is captured in the verse given above, where an animal sacrifice is accepted by God in place of a person to at least temporarily cover over the person's sinfulness or uncleanness so that he may worship God.

What we learn from Hebrews is that these sacrifices were just a shadow of the perfect sacrifice of Christ. The animal sacrifices could never fully and permanently take away sin, but they looked forward to the sacrifice of Christ, whose blood could both fully and permanently take away sin (cf. Hebrews 10:1-14). 

As you read about the various sacrifices, keep in mind that these sacrifices were designed to be "an annual reminder of sins" (Hebrews 10:3). The splattering of innocent blood, the smell of death, the consuming of life in the fire were all to remind the offerer of the awefulness of sin in God's eyes and to cause the offerer not to forget that the sacrifice is but a substitute for himself. It should be his blood, his death, and his life consumed in the fire. 

What is more the animal sacrifices performed in the Old Testament only covered unintentional sins. Intentional sins required restitution or were punishable by death. For instance, no animal sacrifice is prescribed for adultery or murder. These are only punishable by death according to the Law, and the individual is simply left to the grace of God either to eternally save or to destroy.

Let us reflect that apart from Christ, our Subsitute, we should have experienced the excruciating pain of crucifixion, the emptiness and shame of a criminal on display, as well as the forever torment of those offending an infinitely holy and eternal God. Praise God for His grace toward us!

Of the different kinds of offerings, the burnt offering was special in several ways:

 1. It is the only offering that is completely offered (completed burnt up) to the Lord (except for the skin).Leviticus 1:8...and the priest is to burn all of it on the altar. For all the other offerings, only the fat portions were given to the Lord, the rest was consumed by the priest and offerers.

 2. The fire of the burnt offering was to be maintained continuously, day and night. Leviticus 6:13: The fire must be kept burning on the altar continuously; it must not go out.

 3. It is mentioned as far back as Noah. Genesis 8:20-21:Then Noah built an altar to the LORD and, taking some of all the clean animals and clean birds, he sacrificed burnt offerings on it. The LORD smelled the pleasing aroma and said in his heart: “Never again will I curse the ground because of humans, even though every inclination of the human heart is evil from childhood. And never again will I destroy all living creatures, as I have done. (In Genesis 4, Although Abel also made an offering to the LORD, he only gave the fat portions from some of the firstborn of his flock, although this pleased the LORD who looked upon Abel favorably for the offering he gave, it wasn't technically a "burnt offering" because the entire animal was not consumed by the fire)

 4. Abraham was instructed to offer Isaac as a burnt offering to the LORD. Genesis 22:2Then God said, “Take your son, your only son, whom you love—Isaac—and go to the region of Moriah. Sacrifice him there as a burnt offering on a mountain I will show you.”

The LORD gave specific instructions exactly how this offering was to be made, what kind of animal, how and who was to prepare it. Only when the instructions were followed exactly, did it become a pleasing aroma to the LORD. 

We will later see what a mockery King Ahaz (1 Kings 16 and 2 Chronicles 28) and King Manasseh (1 Kings 21 and 2 Chronicles 33) made of the Temple and the system of sacrifices that was instituted by the LORD.  They plundered the temple, set up new altars to make sacrifices to false gods, they even sacrificed their own sons.  All of this was evil before God.  King Manasseh in particular is considered the most evil King of Judah because of the detestable practices that he instituted, however, we see a God who delights more in a person who has a humble heart than any sacrifices that are offered. 1 Chronicles 33: 11-13 So the LORD brought against them the army commanders of the king of Assyria, who took Manasseh prisoner, put a hook in his nose, bound him with bronze shackles and took him to Babylon. In his distress he sought the favor of the LORD his God and humbled himself greatly before the God of his ancestors. And when he prayed to him, the LORD was moved by his entreaty and listened to his plea; so he brought him back to Jerusalem and to his kingdom. Then Manasseh knew that the LORD is God. What a gracious and forgiving God we have.  He doesn't take delight in the sacrifices themselves, He delights in the humble heart of the one who is offering the sacrifices.

Lord, examine our hearts, change our hearts so that it may be a pleasing aroma to you.