Jehovah saith unto Cain, `Why hast thou displeasure? and why hath thy countenance fallen? Is there not, if thou dost well, acceptance? and if thou dost not well, at the opening a sin-offering (chatta’t)is crouching, and unto thee its desire, and thou rulest over it.'

Genesis 4:6-7 (Young’s Literal Translation)

Chatta't is a Hebrew word that can refer to either "sin" or "sin offering" depending on the context in the Bible.  The first mention of chatta’t is found in Genesis.

Cain was enraged when God disregarded his offering of fruit. God Himself however provided Cain with “chatta’t” or a far better sin offering in the form of a lamb crouching or lying quietly at his door. The lamb, of course, is a typology of Jesus.

God also told Cain that the lamb “desires” him. The word "desire" is derived from a Hebrew idiom that describes a man's exclusive and undivided affection for his wife. In a literal sense, the lamb "loves" Cain, and all Cain had to do to be approved by God was "rule over it," that is, sacrifice the lamb. Cain was shown the gospel of grace and was told by God to build his faith in God's provision of righteousness, but Cain preferred to trust in his own righteousness because of unbelief.

Cain could have experienced the same favour with God that Abel did—but he didn't grasp the revelation, which stated that the determining factor of enjoying God's favour was through the offering of the sacrificial lamb. Simply said, he did not take advantage of God's grace by obeying and trusting the means that God has established for anybody to stand right before him. Many individuals, like Cain, place their confidence in their own ideas of what is acceptable to God rather than trusting in His perfect provision in and through Christ. As a result, everyone is reconciled to God without any work or effort on their part, but they are saved just by believing in Jesus.

Jesus is our chatta't—as both sin and sin offering on the Cross. He who knew no sin became sin to make us right with God (2 Corinthians 5:21). He did it by becoming the one and perfect sacrifice for our sins.

Whoever believes on Him will not be put to shame. 

Romans 10:11 (NKJV)

You will not be disappointed if you place your trust in Christ, the Lamb of God who wipes away the sin of the world (John 1:29). Those who understand and embrace God's grace in Jesus Christ are blessed!