If someone incurs guilt: Situations needing a sin offering assumed there was guilt that happened by accident or ignorance. Once someone realized they did something wrong, they became guilty and needed to receive atonement. If someone knew they sinned, they must deal with it. To know what was right and not do it was also a sin (see 5:17; James 4:17).
confess: Offering a sacrifice for sin without admitting guilt was a pointless ceremony. When presenting the sacrificial animal to the priest, the worshiper probably explained the reason for the offering.