First of all only God the Holy Spirit can lead people into truth as they study the Bible. Also the Bible is its own dictionary and guide as we compare scripture with scripture:

• The Spirit itself beareth witness with our spirit, that we are the children of God: Rom 8:16
  
• Which things also we speak, not in the words which man's wisdom teacheth, but which the Holy Ghost teacheth; comparing spiritual things with spiritual. 1 Co2:13
• For precept must be upon precept, precept upon precept; line upon line, line upon line; here a little, and there a little: Isa 28:10
• Then opened he their understanding, that they might understand the scriptures. Luke 24:45