There is no greater Resource than the Bible itself. It is the inspired, 'God breathed' communication of God to people. To gain true understanding of the Bible also known to believers as God's Word, the Bible itself tells us we must know the author Himself.
The Spirit of God or the Holy Spirit is the one who illuminates or reveals it's truth to us. Without the Holy Spirit the Bible is a 'Stumbling Block or Foolishness' to us.
There are many good resources which can help us understand the Bible, but they must never replace the Word of God as the source of truth and life itself for us who have recieved Jesus as our Lord and Savior.