When something or someone is the apple of your eye and it refers to something or someone being cherished above all else.
"Bind them on your fingers; write them on the tablet of your heart." (verse 3)
Meaning, to mark his instructions permanently into your heart. Let God's wisdom lead you through life.
When you accept Jesus into your heart, asking him to get rid of all the sin that so easily entangles us, when you ask him to take your whole life... every part of you believing and accepting his grace, there is a change of heart. A change in your lifestyle.
The decisions you once made should differ from the decisions you make now. You are no longer making choices based on what suits you best but you are living in Christ and through Christ.
Verse 21 says, "With persuasive words, she led him astray; she seduced him with her smooth talk", it continues on to make examples comparing to "an ox going to slaughter, a bird darting into a snare, little knowing it would cost him its life". Sometimes we do this don't we? We have a lapse in judgement (which is normal- we are human) but instead of turning to God for help, we rely on our own strength...which let's face it is not nearly enough. When we decide to make decisions on our own, we start to slip down a slippery slope which never ends in a good place. That is what was happening here. This unwise man was not guarding his heart, the bible says, "a youth who lacked judgement." God was not the apple of his eye. Ruling his own life, pleasuring himself and not connecting with God are what he cared about. It got him into a very bad situation.
The role of a husband from God's perspective is a beautiful, respectable role. A role where a man gives himself WHOLLY to his wife. God gave us sex and other forms of intimacy which are such blessings WITHIN marriage. A marriage is the gospel lived out. This is not just for men though, the same thing can happen for women. Cherish your spouse tonight, remind them how glad you are for them. Remember to keep God center in your marriage, never second place...it just won't work that way!