What does Proverbs 2:18 mean?

The ultimate consequence of sin is death (Romans 6:23). This passage is using the metaphor of a seductive woman to represent sin. In this verse, her house sinks down, implying a slow, gradual process. Those living in a home do not notice the subtle sinking and settling that comes naturally. Yet if just one small portion of the foundation is wrong or is out of place, the house will slowly sink. Often this sinking goes unnoticed until the home is broken beyond repair. This is why David prays in Psalm 139:23, "Search me, O God, and know my heart! Try me and know my thoughts!" God is the ultimate home inspector; He can search out cracks in the foundation and tell us how to fix them.

Another analogy for this point is that of a train, which can go nowhere except where its tracks lead. Sin's tracks lead to death. While it may be relatively easy to stop a train that has just begun to move forward, once it is speeding down the tracks it becomes almost impossible to stop.