You might think the meme in the header image is probably an atheist trying to be as infuriating as possible. I certainly did, as did a Christian who replied to the original comment before me. It's so despicable, I'm almost tempted to censor it, but I'd rather leave it for sake of accurately representing the "other side".
But the truth is, I'm not sure who the "other side" is, in this case. I briefly visited their page, just so I could see if they were an atheist, but atheist or not, they at least seem politically Conservative. The truth is, I still don't know what they are. But I don't need to.
See, if this person is an atheist or other anti-Christian hostile, they have made a ridiculous argument against Christianity that I can at least give a less ridiculous answer to, therefore giving an accurate presentation of the Gospel. If they're a Christian? Well, they have even less of an excuse for ignorance of what I'm about to write.
First, the obvious needs to be pointed out. If one sin is enough to merit death, then a maximum of one sin is enough to make Jesus' death absolutely necessary. Yet we've all done that a thousand times over on a yearly basis from our youth. So even by the ridiculous logic of the meme, Jesus already died for something. We don't need to keep adding to that. If someone pays your debt, you don't run around accruing more debt. That's not just foolish, it's also incredibly selfish, and frankly, ungrateful. Heck, at that point, didn't the one paying your debt do so for nothing? Nothing changed if you're just going to do that.
But that's just using the meme's logic to oppose itself. As it turns out, Paul answered this same objection nearly 2,000 years ago. He begins "What shall we say then? Shall we continue in sin that grace may abound? Certainly not! How shall we who died to sin live any longer in it?" (Romans 6:1-2). And of course he continues to make his case from there. I really couldn't begin to say it any better, and fully recommend picking up the Bible and reading it yourself.
All of that is to say if you think Jesus died for nothing unless you go on sinning, you've missed the entire point of His death. Whoever made this meme, and whoever goes on to share it, is actually demonstrating the exact opposite of salvation. Of course, if they're not a Christian, they're not saved because they reject the Savior, but actually, even a so-called "Christian" with this attitude simply can't be saved. In fact, the same Paul who wrote Romans 6 also wrote Hebrews 10:26-27: "For if we sin willfully after we have received the knowledge of the truth, there no longer remains a sacrifice for sins, but a certain fearful expectation of judgment, and fiery indignation which will devour the adversaries."
In other words, this is a black and white issue. When you turn to Christ, you turn away from sin. It's called "repentance", and you can't be saved without it. Now, that might seem contradictory at first, since salvation is by faith, not by works. But actually, first, it's not a case of sin bars you from salvation. There's nothing you can do, or not do, to gain or lose salvation. Nor is there a specific amount of good or evil you can do to gain or lose salvation. In fact, the entire issue here is faith.
Martin Luther said it well when he said "salvation is by faith alone, but faith will never be alone". Faith and belief are almost synonymous. If I tell you your house is on fire, what are you going to do if you believe me? You're not going to say "oh, thanks for the heads up" and continue reading a comic book. If you have faith, you're going to respond in faith. So, what are you going to do if you truly have faith in Christ? And what does it mean if you're so willfully living in sin that you post memes saying if you don't sin, Christ died for nothing?
It means you don't actually have faith. And for that reason, you're actually the one dying for nothing. See, one day, we all die. And that's when we face judgement. Is sin worth receiving that judgement? Certainly not. I that case, you not only die in this life, but you also experience the "second death", because you did not place your faith in Christ to save you from your sin. You chose sin.
So what we see is whoever made this meme, whether they are a Christian or not, has completely missed the point of the Christian faith. The only reason Jesus died at all is because each and every one of us needs it. Therefore, there is no scenario in which Jesus died for nothing. If a single person is saved, the crucifixion was a grand success. Jesus' death was worth it. The only question that remains is is it worth it for you?