Cain had worked the soil, giving the Lord grain offerings…while Abel kept flocks, giving the Lord fat portions from the animals. On Abel’s offerings God looked favorably, while on Cain’s He did not. But it may have had nothing to do with the physical offerings themselves, but rather in the men’s attitude bringing it before God. Attitude we see here in this verse when God asks Cain where his brother is…(as if God didn’t already know what had happened.) God was testing Cain to see if he would be honest and take responsibility for his actions…but instead, Cain retorted back to God with lies and anger.