Isaiah says "Whom shall he teach knowledge? and whom shall he make to understand doctrine? them that are weaned from the milk, and drawn from the breasts. For precept must be upon precept, precept upon precept; line upon line, line upon line; here a little, and there a little:" (Isaiah 28:9-10, KJV) Paul told Timothy, a young man full of faith and love for God "Study to shew thyself approved unto God, a workman that needeth not to be ashamed, rightly dividing the word of truth." (2 Timothy 2:15, KJV)
Set forth here are invaluable principles of biblical interpretation set forth by Jehovah Himself. God says that there must be careful comparison of scripture to arrive at truth. many christian will admit that the prophecies of the messiah written down in the old testament are beautifully fulfilled in the new. But how did the disciples come to the conclusions? When the Holy Spirit descended at pentacost, he illuminated the minds of the disciples to see the word of God differently. They correctly divided the word of truth and were able to prove and convince both jews and gentiles that Jesus was the Christ.
Spiritual things must be compared with Spiritual, scripture with scripture, line uopn line, principle upon principle.