Each believes that it is the grace of God that opens the door to the opportunity to become a Christian and that once a person accepts Jesus they are born again. From that point on they diverge, one into license to sin, the other into obedience to the law. When this battle moves further into the extreme positions many souls are lost and the only winner is the devil laughing in the background. Understand that each has scripture to back their positions yet at the same time discount the interpretation of those same scriptures the other group uses. When Satan tempted Jesus in the wilderness he too used scripture to try and make Jesus prove Himself.
Scripture is foundation truth with plenty of examples in their application and misapplication.
Only when the word is rightly interpreted can the fullness of that truth begin to reveal itself. The bible is an extensive guide book. Everything you need for a basic understanding is there within its pages. It reveals God's plan of salvation to all who will read its pages. So one would think that if you heard the words that He spoke you would understand the meaning.