The Hebrew word that is translated as "keeper" (shaw-mar), means literally a custodian, watcher, or caretaker. So in Cain's response to God, he is literally asking whether he is his brother's guardian or custodian. Perhaps the statement could even be translated "am I my brothers baby-sitter". So the term "keeper" doesn't mean guide, helper, or aid, but implies a much higher level of responsibility, such as a caretaker or parent.
And the second is like unto it, Thou shalt love thy neighbour as thyself" (Matthew 22.39)