Cain and Abel

“In the course of time Cain brought some of the fruits of the soil as an offering to the Lord. But Abel brought fat portions from some of the firstborn of his flock. The Lord looked with favour on Abel and his offering, but on Cain and his offering He did not look with favour. So Cain was very angry, and his face was downcast.” Genesis 4:3-5
At a first glance, it seems unfair to us why God would reject Cain’s offering. He was a farmer, so it made sense for him to offer to God something that he had produced; Abel was a shepherd, and so he brought an offering from his flock that he had produced.
It has been suggested that God had specified that any offering made to Him was to be a lamb (recalling how He had killed an animal to provide garments of skin for Adam and Eve). If this is the case, then Cain tried to change the rules, but God refused to accept his offering – as was His prerogative to do so. We also read that Abel brought fat portions (i.e. the best parts) from the firstborn of his flock. This would be written down as law by God through Moses (Ex. 13:2, etc.). Abel gave God his best; Cain just brought ‘some of the fruits’.
We also see a difference in response. Instead of repenting and seeking God as to why his offering was not accepted, Cain got angry and pouted. Instead of sorting things out in his own life, he let jealousy take over and he killed his brother Abel (Gen. 4:8).
There’s a lesson here for us. We can see God blessing other people, accepting their offerings, as it were, while to us He seems to be silent. We mustn’t get angry; instead we must seek God and repent. Also, God has specified in His Word how He is to be worshipped (see, for example, John 4:24). We would do well to follow His directions. Both our heart and our actions must be in the right place.