When we accepted Jesus Christ as our Lord and Savior, we accepted a life of service. I think that a common misconception about the “free gift of salvation” is that because it cannot be bought or sold with money, it is available at no cost and there is no price to be paid. That is ludicrous, of course, because that would mean this all-important gift essentially has no value. Jesus paid for your sins with His life, not with gold or jewels. And to take this “free” gift only He can give, you must be willing to make an exchange. Your money is no good, for salvation cannot be bought (see Simon Magus in the Book of Acts for a great example here); you must be willing to give up something of equal value.
Now, if you think about it, who is really getting the best deal? Jesus gave up His own life–the only one that has been lived righteously and without sin–and offered Himself in your place as a sacrifice so that you may be redeemed and stand justified before God. He gave His perfect life for you, and offers you the gift of salvation and of restoration, but there does have to be an exchange. He demands your broken, damaged life of sin as payment. He requires repentance–that is acknowledgment and a turning from your sins, accepting in their place the mercy and grace He has in store for you.
You will either be a bondservant to sin, turning away from Christ… or you will be a bondservant to Christ, turning away from sin. You cannot receive salvation and continue in sin; this is the error of a corrupt conscience and there are many today who think they are saved who in fact are not. They justify themselves, but are not justified in Christ.
For a better explanation than I can give here, I would heartily recommend “The Gospel According to Jesus” by John MacArthur.