Good or God? why good without God isn't enough

These days the terms good and God seem synonymous. We believe what's generally accepted as good must be in line with God's will. Generosity, humility, justice - good. Selfishness, arrogance, cruelty - evil. The distinction seems pretty straightforward. But is that all there is to it? If good is so obvious, why does the Bible say that we need discernment to recognize it?--