While these were God's instructions to the future kings of Israel, they apply to all Christians. Like the king, God expects us to be holy and obey His commandments. The king was to have a copy of God's law for his personal use, to keep it with him at all times, to read God's Word every day and to obey it. Why? The only way to know God's Will is to spend time reading and studying His Word.
The Bible is God's instructions to us for how we should live our lives. A Bible that is not read is useless. The Bible cannot affect your life unless you read it and willingly do what it says.
Applying the Word of God daily to our lives keeps us from sin (Psalm 119:11), gives us joy (Psalm 119:111) and peace (Psalm 119:165), makes us wise (Psalm 119:98), teaches us what is true while pointing out the wrong in our lives (2 Timothy 3:16) and prepares us to do the Lord's work (2 Timothy 3:17). As our understanding of God's Word grows so will our reverence for our Lord, and we will see ourselves for what we truly are -- undeserving sinners who are no better than anyone else.