Leviticus 1-4: Offerings

Exactly one year after the Israelites fled Egypt, the tabernacle is set up and God's glory fills it up.  Then the cloud covered the tabernacle of meeting, and the glory of the LORD filled the tabernacle.  And Moses was not able to enter the tabernacle of meeting, because the cloud rested above it, and the glory of the LORD filled the tabernacle.  Whenever the cloud was taken up from above the tabernacle, the children of Israel would go onward in all their journeys.  But if the cloud was not taken up, then they did not journey till the day that it was taken up.  For the cloud of the LORD was above the tabernacle by day, and fire was over it by night, in the sight of all the house of Israel, throughout all their journeys.  - Exodus 40: 34-38 NKJV

But the tabernacle wasn't just to lead the Israelites.  From there, God calls to Moses and gives directions for offerings.  Burnt offerings and grain offerings were in their history as far back as Cain and Able.  Now the Lord gives them specific instructions on what these offerings should consist of.  He also gives specific instructions on fellowship offerings.  Fellowship offerings, which are discussed further in Leviticus, chapter seven, were not required offerings.  They were above and beyond, just like love offerings are above and beyond the tithe; offerings made by a blessed people to the one who blessed them, acknowledging what God had done.

The next type of offering was one of acknowledgement also, but the sin offering was in acknowledgement of sin:  against God or against their fellow man.  And furthermore, the sin didn't have to be intentional.  Even unintentional sin required an offering, and it was necessary to atone for sin by an individual, by a leader of the community, by an anointed priest, and by the community itself.
‘Now if the whole congregation of Israel sins unintentionally, and the thing is hidden from the eyes of the assembly, and they have done something against any of the commandments of the LORD in anything which should not be done, and are guilty;  when the sin which they have committed becomes known, then the assembly shall offer a young bull for the sin, and bring it before the tabernacle of meeting.-  Lev 4:13-14 NKJV
 
Unintentional sin against any of God's commandments, required someone to bring the matter to the sinner's attention.  The sinner, whether it is an individual or the entire community, had to make a sacrifice.   Once the sacrifice was made, the sin was forgiven.  The tabernacle was not just for leading the Children of Israel, it was also there to maintain a right relationship with God.