If lust does not involve actual physical behavior, why is it wrong?

Proverbs 4:23Guard your heart above all else, for it determines the course of your life.

Once lust takes up residence in our minds, it tends to consume our thoughts, eventually leading to lustful actions.

Deuteronomy 17:17“The king must not take many wives for himself, because they will turn his heart away from the Lord. And he must not accumulate large amounts of wealth in silver and gold for himself.”

1 Kings 11:3He [Solomon] had 700 wives of royal birth and 300 concubines. And in fact, they did turn his heart away from the Lord.

Allowing sexual desire to dominate our thoughts and actions (Solomon had recognized relationships with 1000 women!) will negatively change our behavior and turn our hearts from God. Solomon’s lust eventually led to idolatry and his disrespect of God.

Matthew 5:28“Anyone who even looks at a woman with lust has already committed adultery with her in his heart.”

Mark 7:20-22Then he [Jesus] added, “It is what comes from inside that defiles you. For from within, out of a person’s heart, come evil thoughts, sexual immorality, theft, murder, adultery, greed, wickedness, deceit, lustful desires, envy, slander, pride, and foolishness.”

Luke 11:33-36“No one lights a lamp and then hides it or puts it under a basket. Instead, a lamp is placed on a stand, where its light can be seen by all who enter the house. Your eye is like a lamp that provides light for your body. When your eye is healthy, your whole body is filled with light. But when it is unhealthy, your body is filled with darkness. Make sure that the light you think you have is not actually darkness. If you are filled with light, with no dark corners, then your whole life will be radiant, as though a floodlight were filling you with light.”

James 1:14-15Temptation comes from our own desires, which entice us and drag us away. These desires give birth to sinful actions. And when sin is allowed to grow, it gives birth to death.

Left unchecked, wrong thoughts will eventually lead to wrong actions. If we continue to think about having sex with someone who is not our spouse, our hearts will begin to convince our minds that what we want to do is all right. The Bible says that the heart is “desperately wicked” (Jeremiah 17:9). In other words, we cannot trust our emotions to tell us what is right and good. Instead, we need to trust God’s word, for it comes from God’s heart, which is good and perfect.