Summary: A broken shield cannot protect you.
5 Every word of God is pure: he is a shield unto them that put their trust in him.
6 Add thou not unto his words, lest he reprove thee, and thou be found a liar. KJV
We are warned to take heed if we think we stand lest we fall. How can we do that? We must shield ourselves in the pure Word of God. Just as a diver's suit shields him from the atmosphere of the seas allowing him to move in it without being wet or lacking oxygen so also will the Word shield use from the dirt of the world as we walk through us and allow us to breathe Heaven's atmosphere. It will keep us from falling in the battle as it increases our trust in Him and makes the oxygen of this world as desirable as smog.
It will also help keep us true to God's Word the more we infuse it because it will keep us from adding to or taking away from it by pulling things out of context or doing “evangelistic” preaching which often gets us into trouble by exaggeration or being enslaved to Kodak theology that makes a picture of everything. We will also become less likely to tweak the Word to our liking as the Pharisees did or denying it as did the Sadducees. It is tough enough when a member points out an honest mistake in your sermon, but if you play fast and loose it will be far worse when God calls you a liar because your great sermon was not what He said in His Word, but rather what you wanted it to say. That is a bad spot to be in and a good reason why we need to be sure we are called to preach/teach since we will indeed stand a stricter judgment.