From the "J" Chronicles, "J" asked: "I've heard it time and again in regards to Christianity that deeds are meaningless and belief in Christ is all that matter. In other words, provided I believe, I could opt to become a serial rapist and murderer tomorrow . . . but as long as I believed in Christ, it'd be OK because deeds don't matter at all. . . . Seriously?"
Well, deeds are not meaningless either before or after rebirth as a new creature in Christ. Indeed, it is our deeds (both in thought and action) that would send us to Hell. We go to Hell because of our sins against God. And I would like to reiterate that what hardly anyone has, is a real, deep appreciation for just how serious sin is--even a so-called "small" sin. We do not appreciate the holiness and perfection of God and how astonishingly horrible and damnable out rebellion against Him truly is.
Your question here is a common one from unBelievers; interestingly, it is also one that many Mormons, who believe in a works-based salvation also level at Born Again Christians: "So, all you have to do is say you believe in Jesus and then you can go on and do whatever you want to, like lie, steal, rape, drink and do drugs and you're still saved?"
But Jesus says, 23 “Anyone who loves me will obey my teaching. My Father will love them, and we will come to them and make our home with them. 24 Anyone who does not love me will not obey my teaching. These words you hear are not my own; they belong to the Father who sent me." --John 14:23-24
And this is a description of what actually happens. First off, when the Lord comes to you and He shows you the utter depravity and desperation of your sinful condition, you are devastated. At last, you recognize and understand your need for a Savior. Then, you realize, for the first time the profundity of what He did on the cross, taking your sins upon Himself, so that you can be presented spotless before God. The exchange is mind and heart-blowing. He takes YOUR wickedness and rebellion away, and YOU get to wear His perfect righteousness. From then on, you accept that when God looks at you, He sees His perfect Son in your place, so-to-speak.
As the momentousness of this transaction sinks in, you are filled with a new peace and gratitude and love and devotion to this Savior that becomes a hallmark of your new, ongoing self.
But, you are still in this corrupted body and world, and remnants of your old self--that dead, old sinner and child of devil--still remain, to varying degrees. The Apostle Paul himself complained of a "thorn in his flesh" that he prayed would leave him, but God told Him it was to remain, and it acted as a constant reminder to humility, although God also said that His "grace is sufficient", meaning that, despite there still being some hangers-on from the old, lost self, God's grace, in the end, is going to see the disciple finally perfect and residing in Heaven.
You will find, once you are Born Again, that, while you yet make mistakes--continue to sin--you no longer revel in your sin. You don't seek it out. Your conscience does not bear it. You repent and get back to holy Walk. And as time goes on, sins that use to beset you, begin to fall away. They lose their grip on you. This is commonly known as the process of "sanctification" and I can attest to its validity. So can my wife, and every other authentic "born again" Believer that I have ever met or heard speak of such things.
Another common descriptor of this is when you say, "I am not yet where I want to be (spiritually speaking) BUT I am not where I was!" It is one of the most pleasant and convicting of experiences in the Walk . . . when . . . after trekking for a while as the new "you" . . . you look back and see that, indeed, you are NOT the same person you use to be, in big major ways, as when you lived in unbelief and doubt. Startling things, like being able to love enemies or other difficult people that use to trigger you with resentment and anger. You find you have more tolerance and compassion for others' faults and failings, realizing that you too once were blind and lost.
One of the most pleasantly amusing (to me at least) changes that I see in myself and everyone else I know that is Reborn . . . is that you get an almost insatiable thirst and hunger for the things of God. Honestly, you become what some have called a "Jesus freak." You can't get enough! The things of the world lose their luster and become paltry, foolish and a waste. You crave hearing the Word and all matters pertaining to It/Him. You look forward to Church, or gathering with other Believers. You voraciously want to learn the scriptures, the spiritual teachings, the histories and seek out teachers and preachers who know well how to "divide" it (exegete, explain it) and . . . well, you can't get enough!
Anyone who continues to live in sin and "willfully" break God's commandments after claiming to be saved . . . is what we would call a "false convert." And there are plenty of them about. But being saved is not just saying some formula or claiming Jesus as Lord. It is not even in recognizing who Jesus is. The devils know who Jesus is, but they are not saved.
It requires true repentance . . . and then putting your full trust in Him as Lord of your life. The alternative, and what the devils do, is keeping your SELF as the Lord of your life. This is the crux of the whole thing. Who is your God, your self or . . . God? When God becomes the Master of your reasoning, of your heart, of your purpose . . . you simply do not want to do things that displease Him. You are so grateful to Him and love Him for what He has done, that, like anyone else you have ever loved, only more, the last thing you want to do is hurt or harm or disrespect or disparage or mock . . . the person, the object of your devotion.
Furthermore, regarding deeds, they do continue to have meaning, as the good ones, in His service, are rewarded in Heaven. We will receive extra "crowns" of glory depending on the degree of our sacrifices and works in helping build The Kingdom. All who have Jesus as their Lord will inherit the Kingdom, and their sins are wiped away, but there are additional rewards for some more extraordinary in the faith. There are "many mansions" in the Kingdom. . . .
If someone claims to believe in Christ, but continues to sin and there is no evidence in their life, in there deeds of having been reborn as a "new creature in Christ" . . . then they most likely a liar and false convert. When you believe in and put your faith, your trust in Christ, becoming a new creature, your life will bear the fruits of that rebirth.