Why is it so necessary for a son to watch over, protect, and treasure the words of his father? Well, first it is because a godly father speaks wisdom to his son. Second, it is becasue a godly father speaks contrary to a fallen society - and because of the nature of this world - the messages the son will receive from the world, far outnumber those his father will be able to speak to him.
The father here tells his son to "keep my words." This word "keep" is the Hebrew word "shamar" and it has the idea of keeping and guarding. In one context this word actually means to stand as a bodyguard. Other places the word means a gatekeeper, a guardsman and always has that idea of watching over something with a mindset of keeping it safe and secure. When you look at the context of what this father is about to say, this becomes very clear. The father is about to speak to his son about women - but not just any kind of women - about harlots and loose women.
There is a reason the son should guard these words - and that is because as he grows up - he will be sorely tempted in this area. His own fallen desires and the changes he will experience in his own body are reason enough to do this. The second reason he should act this way about his father's warnings is because at least in today's world - we live in a sexually charged world. The amount of sexual temptation available has exploded in just the last 10 years. There is available to a young man sexually explicit material in a multitude of forms - from the computer to even his cell phone. He better listen to his dad on this one because there is trouble and bondage on the horizon for those who do not listen.
The father calls his son also to "treasure my commandments within you." This term "treasure" means that the son is hiding these things away - storing them up - and putting them in a secret place in his heart. He is keeping them there like treasure - because he knows that they will be needed later in life. It used to be a normal thing for children to be taught the value and the treasure of their virginity and sexuality. These things were considered as gifts to be given to God first - and second to one's husband or wife. The commandments that the father would give to his son consisted of what the Word of God said about sexual matters. Oh, that we would treasure such things - knowing that God only wants to protect us from evil - from problems - and from ruining ourselves in the end. These commandments are not given to keep us from pleasure and joy - they are given to maximize it. Following them not only keeps us from trouble and pain - but they also will bring about blessing for those who keep them.
Oh that two things would happen once again in our society. First, that fathers would take the time to teach their sons and daughters the things of God. That they would take the time to present the biblical standards and protections given to us by God. Second, that children, having heard such things, would treasure them and keep them in their hearts to offer protection and to grant great joy to their hearts in following the Lord all the days of their lives.