Numbers 15

"then it will be, if it is unintentionally committed, without the knowledge of the congregation, that the whole congregation shall offer one young bull as a burnt offering, as a sweet aroma to the Lord, with its grain offering and its drink offering, according to the ordinance, and one kid of the goats as a sin offering." v.24

Read chapter 15
Unintentional or ignorant sins.  What's the difference than an intentional sin?

It suggests a lack of deep understanding of the seriousness of the sin involved. In other words, regarding this sin, the person did not know any better. It includes sins done with a degree of consciousness, an awareness of what one is doing'something done willingly out of weakness' but not sins done deliberately. For instance, the Bible clearly differentiates between manslaughter and murder, and the underlying principle revolves around presumption...Manslaughter is to kill someone accidentally, while murder is to take a life deliberately and willfully. (Bibeltools.org)

It's interesting that this chapter is put here after just having seen them not enter the promised land out of fear and distrust and then all of the sudden starts talking about certain laws.  Maybe it's to show that God will still be with them and require of them even after they disobeyed so many times or also setting the stage for what is to follow in the next couple chapters.  In Leviticus 4 Moses already talked about the law for unintentional sins, but here it's changed a bit as far as what is offered.  It is said that no offering was given for the guilt of unintentional sins.  How of do we feel guilty and want to make up for something by doing something when we've sinned accidentally that caused hurt towards others (physically or emotionally)?  I know I do and maybe this offering helped with the guilt.
David prayed to be cleansed from secret faults (Psalm 19:12).  Paul accidentally spoke evil of the high priest (Acts. 23:5).  What are some secret faults that have been brought to light that you need to confess?