Easy for us to forget God's "Word", and thereby fail to apply it.
1. You need reminding of God's Word. (v12-15) (Remind, memory, remember). It is not just forgetting facts, but rather living accordingly (v9) - the change needs to go on all the time. It is the written word (v15) - the Scriptures - Old and New Testaments.
2. A reliable Word. The centre of the Bible is Jesus. (v16-18). Not stories or myths. If it can be shown the Bible is false, then we ought to give Christianity away. But it is the word of eye-witnesses. And the word is from God, through His Spirit. (v21). The Bible is God telling us straight from His mind what He wants.
3. We need to pay attention to it. (v19) It is our light in the darkness of this fallen world (without Christ).
Four short applications: (a) Read the Bible. (b) Avoid easy alternatives, ie, substitutes for the Bible. (c) Apply it - expect God to change you. (d) Keep it central in our ministry.