To what extent should we watch over God's Word in our lives? How much of a love and a desire are we to have for it? That is the subject of this proverb - and the imagry used here will help us to grasp it and know the depth of love and care with which we should hold God's Word.
Watchfulness and care is how we should keep God's commandments. They will give us life. Thus we want to protect ourselves from disobeying them - from forgetting them - from being distracted from obeying them. But to what extent should we do this? That is where this proverb uses a great picture to teach us.
How well do you protect your eye? If you are like the average person you will protect your eye almost instinctively. When something is coming toward your eye - you will close it - and most often will cover your eye to keep it from being injured. One of the ways that a raven determines whether something is dead or alive - is that it pecks at the eye of the animal. If the animal does not react to protect its eye - it is dead. So, we see that the manner in which we should protect God's Word in our hearts and minds is with an almost instinctive defensiveness. In the same way we would protect our eyes from injury - we would protect the Word from being taken from us - from being the instruction for how we should live each day. This is what is meant by keeping the teaching of God's Word as the "apple of our eye." This phrase is a Hebraism for keeping the very pupil of our eye.
Watch over God's Word - watch in order to obey and honor God in how we deal with it. Watch so that disobedience and disregard for it are absolutely out of the question. Watch over it so that you would prefer having your eye poked out than to walk in a way that would be contrary to it.