Don't pretend like you have never done it before, because we are all guilty of doing this at least once (but probably more than once) in our lives. We treat the Salvation given to us by Jesus Christ as a "Get Out Of Jail, FREE" Card. Now, right away, I may have people jumping on me and saying that this analogy is correct because we can't work our way into Heaven and the gift of Salvation is free. Well, I have no dispute there. But that's not all it's about.
First of all, think about the card in general. Think about its use. Notice the smaller set of words underneath:
THIS CARD MAY BE KEPT UNTIL NEEDED OR SOLD
And here's where the problem comes. We look to Christ's Salvation only when we think we need it. But until then, we continue to "walk in darkness" (as John talks about). Maybe you have friends who are not Christians, and you give no indication that you are a Christian. You use foul language, you laugh at their crude (sometimes even God-mocking) jokes, sometimes you even add a few jokes of your own. THEN, something bad happens in your life and you go running to God with your little "Get Out Of Jail, Free" card and start begging Him to help you. OR, maybe your friends know you're a Christian, but you've purposefully told them a number of times "Well, I'm not really strict" or "I'm a loose Christian", and you proceed to let words and jokes come out of your mouth that are grieving the Holy Spirit Who dwells in you. Do you understand that? We Christians really do take that for granted. The Holy Spirit is within us. And when we sin, we are grieving Him, and I think, in a lot of ways, it may be worse for this Member of the Trinity because He is seeing us commit these sins firsthand.
As mentioned above, John tells us in his first epistle:
"If we say that we have fellowship with Him, and walk in darkness, we lie and do not practice the Truth." 1 John 1:6 (NKJV)
It is not enough to just have Salvation. If we profess to be Christians but treat Salvation as a monopoly card, in other words not taking advantage of Salvation until the very End, thereby letting us live our lives however we want, then we are walking in darkness; a.k.a. Satan's Territory. A place where Satan (and anyone else for that matter) pretty much has the right to call us his "children" because if we're in Satan's Territory it means we're acting like Devils, and as that old saying goes: "Like father, like son."
The Apostle John's letter was written (including the above verse) largely to a dangerous heresy called Gnosticism. Now Gnostics held to many heretical beliefs, but among their beliefs was the idea that they could do whatever they wanted to their bodies because sins committed could not affect the spirit. So even if they led the most sinful life in the history of the world, they would still get to Heaven. Now we look at that and say "That's terrible!" But in actuality... we have to admit that that doctrine is what many of us practice. Christ's Salvation is our "Get Out Of Jail, FREE" Card, so it doesn't matter what kind of life we live. In the End when we stand before God, we simply give Him the card and He opens the gateway of Heaven for us, saying "Well done, good and faithful servant."
I hope you're seeing something wrong with this picture. Notice what God says to us: "Well done, good and faithful servant." We are to serve God with our lives. Now while works do not get us into Heaven, they do play an important part in our service to God. James tells us:
"Thus also faith by itself, if it does not have works, is dead." James 2:17 (NKJV)
Work for the Kingdom. Serve God. Start acting like His children! Otherwise, Paul tells us:
"He himself will be saved, but only as one barely escaping the flames." 1 Corinthians 3:15 (NIV)
Doesn't that sound awful? I mean it's great that this person would still be Saved... but I don't know about you, I don't want to just barely escape the flames. I want to be as far away from them as possible! So all this is not to necessarily say that you are not Saved, but you are clearly in a lot of danger. You are exactly at the reaching-distance of the Devil, and believe you me, he will grab you and pull you down lower.
Throw out that "Get Out Of Jail, FREE" Card. Don't just apply Christ's Salvation at the End. Apply it to your life now. And let the Holy Spirit begin the Sanctification process as you stop walking in darkness.
"But if we walk in the light, as He is in the light, we have fellowship with one another, and the blood of Jesus, His Son, purifies us from all sin." 1 John 1:7 (NKJV)