Why was God upset with Cain's Offering?

I have always been perplexed by the story of Cain and Abel. It never made sense to me why God was upset with Cain's offering. I guess the confusion begins with thinking the problem was what Cain offered. Why should God be upset with an offering of the fruits of the ground. the answer i always got was that the one concerning the symbolism of the lamb and his blood and it pertaining to Christ but why would God hold Cain accountable for a symbol he hasn't even revealed yet. they weren't told to sacrifice till many many years after Cain's death. and then there is the argument that God was not upset with Cain's offering just that he favored Abel's more but none of these really explain anything just they make God more mysterious than he needs to be. i think too often people don't understand something or don't see something right away, and rather than going on a search to figure it out or tell the person who's asking that they don't know they cop out and say God moves in mysterious ways and we may never understand. And while this is true God has made many things known and it is our responsibility to search for the answers because we are told to have an answer for those who ask. nothing turns people away more than a cop out answer that they've already known. so i have gone many years not understanding and completely perplexed but what to me seems to be a rather large injustice upon Cain. and all the answers i have come across provide no application for my life. but a couple of Sundays ago i was in chapel and the chaplain was talking about the story of Cain and Abel and finally i found the answer i was looking for. The answer is in paying attention to the details of the story. if you notice with me that the verse says In the course of time Cain brought some of the fruits of the soil as an offering to the LORD Genesis 4:3. notice the verse says that Cain brought an offering to the Lord so obviously he felt it was necessary and that God had control over his fields. many of us are like Cain and we feel the need to offer to God a portion of profits. and when you look at it on the surface Cain has done nothing wrong he has done a good deed many people would say which is probably why i have struggled so hard with this passage but if you pay closer attention to the details of the verse it says Cain brought SOME of fruits. this is the problem right here. God did not have a problem with what Cain offered but how Cain offered it. Lets look at the next verse to better analyze this thought. But Abel brought fat portions from some of the firstborn of his flock. Genesis 4:4 Abel brought an offering from the firstborn, or the best of his flock. So God looked with favor upon Abel not because he brought lamb but because he took the best of what he had and he offered it to God. Cain on the other hand just grabbed what was most convenient for him at the time. God is upset with Cains attitude. And with this answer i found so much more application to life. it is a story not about what you should offer to God but how you should offer it to God i think too many people myself included give whats most convenient to them at the time say a couple of bucks or even 10% of their earnings not to forget volunteering time to work on projects but only at a time that is convenient to you. God wants us to give our best and give it selflessly. the entire purpose of Giving to God is not because he needs it but because he wants our attitude to be like his. Giving and helping even when its not convenient for us thats what the story of the poor woman who put all of her money into the offering is about. its about here attitude towards God, it was inconvenient for her to give all her money away but she did it anyway. We need to come to offerings with a correct attitude that God Gave to me the very best of His so i will give back to him the very best of mine. You can offer to God everything you do everyday. When you wake up in the morning offer it to God when you Go to work in the morning Dedicate it to God when you are at work Do your very best give 110% because you are offering it to God because whatever you do you do it for his Glory and then you have pleased God with your offering of something more than money or time you have offered him your life in service to him gladly.