The Book of Leviticus is the record of the Old Testament Law - commandments and rules for living, sacrificial worship expectations, and the foundation by which we were to come to understand that a penalty for sin was to be paid. In other words, the Law acts as a means to help us understand why the sacrificial death of Christ was necessary - it points us toward his work of what we call "atonement". To understand atonement, we must understand why it is necessary. As pointed out numerous times throughout scripture, man has a difficult time living his life "without sin" because he has a sin nature. He has free choice, and as a matter of choice, he sometimes chooses things which are a violation of the way God would want him to live. When this is the case, this is referred to as "sin" - better known as "missing the mark". In other words, try as we might, we don't always hit the target!
If anyone sins by breaking any of the commandments of God which must not be broken, but without being aware of it at the time, the moment he does realize his guilt he is held responsible. (Leviticus 5:17-18 MSG)
I don't want us to focus on the Old Testament Law as a means of righteousness, but hope we can see God's intent in giving it. He was laying out the foundation for us to recognize the need of a "sinless" or "spotless" offering on our behalf. Plain and simple, he was pointing us toward Christ. The little lamb, turtle doves, and rams used in the sacrificial offerings of the Old Testament temple worship, atonement sacrifices, and the like, were simply "fore-shadowing" the sacrificial death of Christ on our behalf. That said, then we are free to see what God says about our sin.
As we examine what God has to say about sin in scripture, we find there are not so much "degrees" of sin (as ALL sin is sin), but that sometimes we are totally aware of our sin and other times we almost sin without really realizing we have. I grew up in a church environment which promoted the "degrees" of sin - some were "menial" and others were quite "grievous". If we go back to scripture as our source of truth on this matter, we will see ALL have sinned, ALL sin matters, and ALL sin requires an "atoning sacrifice". This idea of "degrees" of sin just doesn't hold up under our examination of what scripture outlines.
Since there is validity to this idea of us "knowingly" and "unknowingly" engaging in sin, maybe this is where we start. Those things we know better than to do, but do them anyway - these are a big deal. God doesn't ask for our obedience to be at our convenience, but rather for it to become a spontaneous response of our heart. When we struggle with obedience in a particular area of our lives, he doesn't expect us to resist the temptation to sin in that area all on our own. He gives us the support of his Holy Spirit, others which whom we can enter into accountability relationships with, and the wisdom of the Word to guide our actions. Those areas were we struggle without even really recognizing our struggle are sometimes not evident to us unless someone else points them out, or perhaps we get that "twinge" of conviction when we hear a good teacher, or read something we may have overlooked in scripture.
What God wants us to see is that both require our attention - when we "become aware" of our sin, we have a means by which we can deal with our sin - Christ's sacrificial death on our behalf. ALL sin required his death. ALL sin is subject to the same "scrutiny" by God. ALL sin leaves us "at odds" with God - we aren't right until that sin is "under" or "covered" by the blood Christ shed on our behalf. What is most important when studying the Law in the Old Testament is not the rigidity of the sacrificial means for atonement, but that atonement is provided by means of God's grace. The sacrifice was just a means of us connecting our actions with the penalty needing to be paid. It is not much different than us connecting our actions with the penalty which was paid on our behalf - Christ Jesus. He is our "means" of connection between the "wrongdoing" of our sin and the "right-setting" of our lives through the perfect action of his sacrifice.
Although "degrees" of sin don't really exist, the means by which sin is dealt the final blow in our lives is already accomplished - even though it may not be fully revealed by our actions today. Christ's sacrificial death on our behalf was "complete" on our behalf - past sin, present sin, and all future sin. His actions were complete - meeting ALL our needs for atonement - the known sin and the unknown; the "biggees" and the "wee ones". Just sayin!