The depravity of man means that everyone is born a sinner. Psalm 51:1 "Behold I was brought forth in iniquity, and in sin my mother conceived me." The depravity of man doesn't mean you can never do something good, but it means no man can ever do anything whatsoever that is completely acceptable in the sight of God. After all, the security system did some good, but it wasn't acceptable enough to keep everyone out. We too can do some good things as well, but nothing is completely acceptable to God. Even the good things we do are like filthy rags. Romans 8:8 "Those who are in the flesh cannot please God." Nothing we do as sinners, wether good or bad, is acceptable to God, because nothing we do is for God. The only way we can truly please God is through faith. Now the security system cannot fix itself, and neither can we fix ourselves. We are so corrupted by sin that on our own we cannot even seek God. Romans 3:10-11 "As it is written: There is none righteous, no, not one; There is none who understands; There is none who seeks after God." God is so gracious He comes to us. Revelation 3:20a "Behold, I stand at the door and knock:" All we have to do is answer Him.
Now that we've looked at what total depravity means, I would like to share the difference between total depravity and utter depravity. Total depravity means everyone is helpless in sin, utter depravity means you are the worst you can be. R.C. Sproul says "Obviously some people are far more wicked than others. Next to Saddam Hussein or Adolf Hitler the ordinary run-of-the-mill sinner looks like a saint. But if we lift our gaze to the ultimate standard for goodness - the holy character of God - we realize that what appears to be a basic goodness on an earthly level is corrupt to the core.” Total depravity is like comparing ourselves to God's law, everyone qualifies as a sinner, utter depravity is like comparing ourselves to others, such as killers, and thief's.
Beyond the difference between total depravity and utter depravity, lets look at the significance of the depravity of man. The depravity of man shows us our need for a savior, and that we can't save ourselves, but salvation is completely the work of God. As I mentioned earlier, the only way we can please God is through faith. Ephesians 2:8 "for by grace have ye been saved through faith; and that not of yourselves, it is the gift of God;" Also we see through the depravity of man how much God loves us. For He sent is Son Jesus to die on the cross, while we were yet sinners. Romans 5:8 "But God demonstrates His own love toward us, in that while we were still sinners, Christ died for us."
The depravity of man means everyone is flawed, and no one can save themselves. We are all flawed like that multi-million dollar security system, and we are in need of fixing. Jesus Christ is the perfect answer to our need, in that He took all our sins away when he died on the cross. Time is short, and you won't always have the chance to repent and be saved. Hebrews 3:15 "Today when you hear his voice, do not harden your hearts."