A theist believes in the existence of a god or gods. He may or may not believe in the Christian God. He chooses who to believe as god or gods according to how he personally perceives the character of that god. A Christian believes the existence of God who created everything in the universe as He was revealed from the Bible. This Creator-God made man the crowning glory of His creation and gave dominion to the world He created. But man sinned against God and therefore brought to himself and the whole world a great curse. Man was now destined for punishment. But God, in His mercy, sent His Son, Jesus, to die on the cross to provide for a payment for man's sins. The Christian theist, because he understood how he has offended God, gets right with Him through repentance and faith on the finish work of Jesus at Calvary. He then lives his life for the pleasure of God.
Now, why am I happy that I'm a Christian theist? Let me give my reasons one by one.
First, in believing in the biblical God, I do not put myself in a possible state of regret. What do I mean by that? Because I chose to believe in the God of the Bible and through reading of His Word have understood His full character (that aside from being a loving, gracious and merciful God, He is also holy and just), I get right with Him for all my offenses against His Commandments through the way He has provided which I have stated earlier. I then live according to how He wishes that I go about life which He clearly states in His Word. If, when I die, there really was no God and therefore no afterlife, then I have nothing to regret because, first, it was my joy to live for this supposed non-existent God, and second, I really do not have any chance to feel regretful as I don't exist anymore after this life.
Contrast that to an atheist who adamantly believes that no god, including the Christian God, exists. He lives life according to how he wishes to live it, devising his own standard of morality according to how it suits himself. If he enjoys lying, cheating, having sex with numerous partners, etc., then there's nothing wrong about it because, in the first place, there's no God out there that he'll someday give an account to. Then the atheist dies and finds out there's life after death. He also finds out that yes, the Christian God exists and He has accounted for every time the atheist has offended His Commandments that He had made known through the Bible. The atheist now finds himself in big trouble. He wants to correct his mistakes but it is too late. He then spends his eternity in Hell together with those that disregarded God in their lives.
Now, be the judge. Who has a bigger problem between the Christian theist and the atheist if any one between them ends up wrong with their belief?
Second, a Christian theist lives for a higher and eternal purpose while an atheist lives for himself and for now. When a person becomes a Christian, he becomes selfless. If you find someone who calls himself a "Christian" but is selfish in his ways, that is not a true Christian. The true Christian, from the moment he became a child of God, starts to go through a lifetime of divinely engineered transformation that makes him God-centered from being self-centered. To be God-centered means to live for the pleasure of God. He desires to obey God in his life even if at times, obeying God is difficult. All he knows is that his obedience is done for the One who loved him so much that He gave His life for him at the cross. He lives, not for the purpose of making himself known to others, but for the purpose of making God known to others through his life. And because the purpose for his actions is to please God, others benefit from his ways because he obeys God's command for him to also love his neighbors. He also understands that although obedience to God in this life is not an easy task, what awaits him in Heaven will someday outweigh the hardships of this life.
The atheist is different. He lives solely for himself. He engages in what feels good for him even if others don't see their actions as "right". His actions are not as far-reaching as the actions of the Christian theist. His concern is for his own happiness in this lifetime. And even if he does good things for others, he does these things so that he'll feel good about himself. Sometimes he does good things because others around him tell him to do so and not doing so will give him a bad reputation. In the end, when the atheist dies, so does every enjoyable and good things that he has done in his lifetime.
Third, a Christian theist has a better understanding of life and the circumstances that come along it. A true Christian believes the Bible when it declares that God is sovereign. He also understands what it means for God to be sovereign... that God has a purpose for both everything that He allows to happen and events that He orchestrates to come to past. Although a Christian would, at times, feel disheartened when trials come his way, the moment he looks at things with eyes of faith, he is strengthened to continue trusting in God. And although he may not fully understand at the time of his trial God's purpose for giving it, he still has peace in his heart that God knows what He's doing. This is what the Bible describes as the "peace that passeth all understanding." And this peace, for the Christian, is true for he has experienced it. Instead of asking "why did this happen?", the Christian asks God "what do you want to be accomplished through this trial?"
The atheist's hope during circumstances is on himself and on others. Well that's a lot of help already considering the many abilities of man, right? Yes, until man reaches his limits. The abilities of man will not in any way match even an ounce the power of the sovereign God the Christian theist believes in. You can even add what technology can offer as help and yet, there are circumstances that will still leave a person helpless. Another consideration is that whatever abilities man has, God was the one who gave them to him. Therefore, God also has the power to take them back just like what He did with king Nebuchadnezzar in the fourth chapter of the Book of Daniel. And because the atheist does not believe in an all sovereign God, he will always have no explanations for why circumstances come to his life or to other people's lives. Questions of "why?" will never have an answer for the atheist.
Fourth, the Christian theist has an easier task of proving God's existence than the atheist proving that He does not exist. The burden of proof is not on the Christian theist. It's on the atheist. Why? Because the atheist must search the whole universe to really prove that no God exists. He needs to look at every corner, under every rag that's on earth, every closet, every building, every star, planet, moon, galaxy, etc., to come to the conclusion that "yes", there is no God. Until he has done that and has proven 100% that no God exists, the atheist actually remains an agnostic (not sure of God's existence) rather than an atheist (someone who is 100% sure that no God exists). That's one great task considering that up to now, they haven't even proven that the evolution of man is a fact. If man really came from apes, and that if the missing link is found, all doubts for evolution will disappear, then you can expect millions of in-between species out there of apes and man. But why, until now, all they have to show are dummies in science museums? And the evolutionary atheist claims that everything is material. If that's the case, how can they explain how chemical soups after the big bang were able to create non-material things like laws, logic and the sense of right and wrong. If everything is one big accident, then how come they have a natural desire to love and care for people like family members who are, in the first place, "just accidents"? Ah! These, my atheist friends, are transcendent attributes of God. So when you use logic, you are actually proving God to me as chemicals do not produce logic. You really have a great task ahead of you in proving that God does not exist, my atheist friend.
The Christian, on the other hand, does not need to search the whole universe to prove that God exists. Only one proof of Him will settle things on the Christian theist's part. The design and order in the world are enough proofs that God exists. How can order and design come out of such a chaotic explosion? Even mathematical probability has proven so many times that order and design in all of the universe is impossible from a big bang. As what was mentioned in the previous paragraph, non-material things like laws, logic, sense of right and wrong are other proofs for the Christian theist that God exists.
But the most important proof for the Christian is experience. We, Christians, have experienced God in so many ways. I am not talking about the "to see is to believe" kind of experience. I'm talking about the kind of experience that only God can give a person. First, was when He removed the guilt for our sins when we became His children. Then, when He slowly brought change in our lives from sin-loving people to God-loving people. Then, God continues everyday by how He helps us in trials and sufferings. Every promise He has from His Word comes alive as we continue to trust Him. The experience is true. One that atheists have not experienced. This is the reason why atheists will never understand why Christian theists will not turn away from believing God's existence no matter how "intelligent" atheists think their arguments are against God's existence. This is why Ray Comfort said that "a person with knowledge is at the mercy of someone who has experience."
Let me give you Ray's illustration. A child was told by his mother not to touch a flat iron attached to an electric outlet because it will burn his skin. The child, at that point, has gained knowledge. But out of curiosity, the child touched the flat iron. He felt how it burned his skin. At that point, he not only has knowledge. He now also has experience. Suppose a scientist comes and with very scientific explanations tries to convince the child that the flat iron is not really hot. Do you think the child will believe the scientist? No, of course! His experience has proven that the flat iron is hot.
Atheists! We have experienced God! You may think of us as crazy for believing what you claim to be such "unscientific belief". But that's okay. We know we're right in believing God because we have experienced Him. We will also pardon you for not believing us because we know that you will never understand us because you haven't experienced God. But we do hope that one day, you will come to the point that you'll desire to also experience God. I'll pray that day will come to you because I can assure you that if you just humbly come to Him with repentance and faith, He will never fail to make you experience Him in the same way that Christians have experienced Him. Then, and only then, will you understand why I'm happy that I'm a Christian theist.