Cain had a nonchalant attitude towards his worship and service of God. He never wanted to do his best for God, he wanted to be allowed to put in whatever is good to him. Hence, his sacrifice and worship were rejected.
As Christians we are in a blood covenant with God. This covenant was established by Christ Jesus and sealed with His blood.
In this Holy covenant is an agreement; God has His own role to play and we as Christians, have our own role to play. God’s ability to keep His part is the faithfulness of God to His Covenant.
Show me a Christian who fears God and I'll show you a man who serves God in truth. Do we not know that David whom God attested to be a man after God's own heart had one secret? He feared God! For He said, "The LORD forbid that I should do such a thing to my master, the LORD's anointed."
I don't want Christians to be ignorant that the name of Jesus is more powerful in the tongue of those who are better grown and developed in the Spirit. Principalities pay no respect to titles or position; but men of sizable heights in the Spirit they listen to.