What was wrong with Cain's sacrifice?

As a little boy, I have often been told the extra-Biblical story of how Cain brought bad fruits and yams to offer sacrifice unto God. While Abel brought good Rams and goats for his own sacrifice.
Growing up, I found out that Cain did not actually offer bad produce unto God. He simply offered what he had. The question is that, what was wrong with Cain's sacrifice?

I know your mind will quickly go to the 'state of his heart!' which is true. But beyond that, I think Cain did not use the correct 'code' to access God's presence.
Abel offered animals for sacrifice which must bring out blood. Representing the blood of Jesus Christ today! Cain was offering 'sweat' , 'labour' representing works today.
Let me tell you, there is no amount of good works a man can do today that can appease God. The only 'code' God recognizes is the atoning blood of Jesus!
Have you being to Jesus for the cleansing flood?, are you washed in the blood of the lamb? If not so, your sacrifices might be like that of Cain. all your efforts, prayers, fasting , mountains climbing, valley going, giving will not amount to anything except you come through the blood. I am telling you the truth!
It is my prayer that God will open our eyes to see things that matter! Thank you.. Follow me @petoz for more insightful episodes