We can look at the concept "free ride" in many ways. Grace by definition is something that is free in the sense that we can't earn it, we can't buy it, we can't deserve it, and there's no merit in us by which God bestows his mercy upon us. Anytime God dispenses mercy or unmerited favor, which is how we define grace, he's doing something that he has no obligation to do. I'm convinced that when we receive the grace of salvation, our eternal destiny is secure. I'm convinced that once we are clothed with the righteousness of Christ and have his merit imputed to our account by God (which is an act of God's grace) and we are redeemed, then I believe we are virtually guaranteed eternal life. In other words, I don't think that a Christian can lose his salvation. I say this because I'm persuaded that God has promised he will keep us to the end. If it were up to us to persevere, to hang on, and to be faithful and obedient to the end in order to be saved, I don't think any one of us would persevere enough to merit salvation. But God promises to finish what he has begun.
Does that mean it's a free ride? So often the concept of free ride means that since God has given me grace and since God has started this work and he promises to finish it, there's nothing left for me to do. I can do whatever I want. I'm saved and I don't have to worry about a thing. It's free from here on in, I'm on a roller coaster without any brakes, and I can do whatever I want. I can sin as I please and enjoy it the rest of my life. It's a license to sin.
However, the apostle Paul points out that where sin abounds, grace abounds much more. That is to say, the more I sin the more I see the grace of God because more grace is necessary for me to get into heaven.
Some people say that if the more you sin the more grace you get, the best thing to do is to keep sinning and that way you'll get more grace. Paul asks the question "Should we continue in sin that grace may abound?" How does he answer it? He says, "God forbid." Sinning all the more is a totally opposite response to one that is pleasing to God. As a matter of fact, the more grace we receive, the more we are to be moved toward a sense of gratitude; the more gratitude we experience, the more we should be moved to the pursuit of righteousness through obedience to the law of God. As Paul says elsewhere, "We're to work out our salvation with fear and trembling" because God promises to work within us to will and to do what is right. But along with God's grace comes the challenge for us to fight with all of our might to resist the temptations of sin and to pursue a life of righteousness and obedience. My salvation doesn't depend on my obedience, but my obedience is to be a response to that grace of God.
~ R.C. Sproul, "Now That's a Good Question!"