"The way of Cain" describes any religious system that attempts to earn God's favor by works and rituals rather than reliance on God's grace.
"The way of Cain" says there are many paths that lead to God rather than one path.
"The way of Cain" refers to any individual who attempts to approach God on his or her own terms rather than on God's terms.
Abel's sacrifice was accepted by God because it was made according to God's instructions. Cain, however, tried to approach God in his own way and was rejected by God (Genesis 4:3-5). From that point on, Cain became a symbol of those who try to approach God on their own terms.