I teach a series entitled "Passion with a Purpose". In the second session I cover the subject of "Acceptable Worship". Let me say something we must all understand right at the beginning: The way we worship and approach God MATTERS to Him. God establishes the protocol for approaching Him and has laid it out in His Word.
The real lesson in this story is that when God accepts your offering, He accepts you! When He does not accept your offering (Cain) He doesn't accept you! Pay close attention to this scripture. "Ascribe to the Lord the glory of His name; bring an offering and come into His courts." If the worship we present to God (in group or individual worship) is acceptable to God - we get in! When we get in to His incredible Holy Place we are never the same! He eagerly waits for His folks to "enter in" to His presence...with acceptable worship. Remember, the way we approach God and what we offer to Him does really matter.