In a word: Jesus Christ. Fine, two words.
That's not to say God the Father and the Holy Spirit are any less important, but let's face it; if Christ hadn't done what he did, I wouldn't be here now writing this. It would be a waste of my time.
Because of humanity's innate sin nature as a result of the age-old curse brought upon us by the infamous Adam and Eve, we are in and of ourselves unable to do anything good in the sight of God. God is holy, righteous, just, and pure; we as human beings are exactly the opposite. We're covered head to toe with this sin "slime", and there's no way we can totally rid ourselves of this problem on our own.
The ancient plan looked like this: In order for you to atone for your sins, the high priest would have to get up early and make blood sacrifices to God every day. Plus, it would only work if you were a Jew - if not, tough luck). The law was the most important thing back then, not that it's illigitimate now, but way back when, keeping the Ten Commandments was of the utmost priority.
Then came Jesus, the much-prophesied Messiah whom everyone was anxiously awaiting the arrival of. He was God incarnate in the form of a man, and he lived on earth for better than thirty years while demonstrating love to mankind, performing dazzling miracles, and gathering disciples. He was not just a teacher, He was not just a prophet, and He was certainly not just a good man. He was God. Jesus frequently proclaimed His deity. If He was just a good teacher who claimed to be Deity, He is either a lyar or insane. Oddly, people don't think He is any of the three, which is an impossibility.
Jesus Christ was betrayed and killed, a death by crucifixion. You've seen all the pretty Renaissance paintings with Christ sitting there reading a book or something, His head aglow, puppies and kids playing in the foreground, ad nauseum. I can assure you it was quite gruesome. When you are crucified, the first thing that happens is you are tied to a rough, splintery piece of wood and forced to lie on it. Of course, beforehand Jesus had been scourged with whips which flayed his back wide open. So now you're lying on this sharp chunk of wood, and they start hammering spikes through your palms and ankles. That would sort of hurt a little bit, I think. After you've been attached to the cross, they will lift you up on the cross and ram it into a hole in the ground. I imagine that would be quite painful, ripping into your tendons and ligaments a little bit more. So there you hang on there, naked with your arms spread out and head down. Kind of an embarrassing situation, too. After a while, it will become very difficult to carry on breathing, and as the fatigue sets in, your lungs will fill with your own body fluids and you will drown. That's how you die on a cross. By the time they are done with you, you will literally be an unrecognizable blob of bloody flesh and bone fragments.
That is why we cherish Jesus Christ so much - because He loved us so much that He was willing to go through infinite agony to pay off our debt of sin for us. There was no way we could have ever done that. And now, since we've been paid for in full with Jesus' own blood, all He asks of us is to live for Him. And if we confess that we are wrong and recognize what He did for us, He'll forgive us and make us holy (I John 1:9). On top of that, we will be given the right to be Children of God, joint-heirs in Heaven with Christ. How can we refuse that deal? All we have to do is put our faith in Christ and we have it made for eternity. Can't beat that, eh?
However, it's a rule that the time we spend as Christians on earth will not be easy. It's our task to open the light to others who have not yet seen it, and to bring them to the truth. We'll undergo ridicule and persecution for what we believe, yes, even in this land of so-called religious freedom. But that comes with the territory. Are you ready to give your life to Christ? He suffered a whole lot more than we'll ever have to if we trust in Him today. If not, you're taking an awful gamble that you'll still be around tomorrow...
We ask you now, please think it over. This decision will change your life forever, and you will not regret it. Accept Christ for what He has done and for Who He is: God, who died for mere man.