To the OP.
This is the most personal and difficult question you can ever ask a believer. There’s a quote that comes to mind–sorry I don’t remember who said it and I can only paraphrase: To those that believe no proof is necessary and to those that don’t, no proof is possible.
Every devout Christian I know has had some personal experience that has convinced them of the truth of Christian teachings. We call it the Conversion Experience. I’ve done quite a lot of reading on this and noticed that all conversion experiences follow a basic pattern.
Born into faith.
Learned basics from parents/Sunday school/Catholic school nuns.
Never really “got it”.
As teen or young adult drifted into secularism.
Something happens: meet someone of faith, have kids, read a book, hear a talk, experience some tragedy.
Suddenly know that it is all true.
Remember rudimentary faith and decide to do research and learn more.
Explore teachings, seek out others who’ve had similar experiences.
There are many variations on this theme. Some never knew any faith until they experience their tragedy. Some drift out of one faith tradition and find “truth” in another. Some explore many faith traditions and find the fullness of truth in one particular expression of the faith. Some find their way back to the faith of their upbringing. Some never leave at all but experience a profound confirmation of their faith at some point. The last is rare for Catholics these days because of the poor catechesis of the last four decades.
In my case, I read a book in my thirties (“Surprised by Truth”, Patrick Madrid) and it forced me to admit that I’d been taking my faith for granted and I resolved to take it more seriously. I began to learn. Now I’m almost 50, I’ve read and accumulated a library of books that cover one wall in the parlor and I don’t feel like I’ve even begun to scratch the surface. I’ve grown in my prayer life and yet have a long way to go. I go to Mass a few times a week in addition to Sunday, and I feel like there is much more there that I’m not tapping into. I go to confession at least once a month and I am still a pitiful sinner with very little discipline. But the point is that now, at least, I’m on the right track. God’s most beautiful attribute is His Mercy. I count on it.
That’s my experience. No one else will identify with it and it won’t convince anybody. But, without diving into the philisophical melee that makes up the majority of this thread, there are many ways to “prove” that God exists. However, if you are sceptical at every point, then nothing will convince you. What fits best with the way I think is to start with history.
If you accept that Jesus existed–there is enough historical evidence to make this point easy to accept–then he must be either a liar, a lunatic or The Lord. But I’m getting ahead of myself. Jesus existed. He had followers. These followers made amazing and bizarre claims about the life, death, resurrection and ascension of Jesus. What did they have to gain by maintaining these claims if they were not true? All but one of the twelve were martyred. None made any worldly gains by their claims. They were hunted and chased all over the world. Something like the first 36 Popes were martyred or died in exile. Just everyday Christians were imprisoned and tortured and executed for three centuries just for following the teachings of Jesus.
Jesus claimed to be the Son of God, sent to Earth to redeem mankind from sin and death. He could have been lying to his followers. If so, he wasn’t a very good man, was he? He caused the suffering and death of himself and thousands of followers and for what? What did he stand to gain by lying, especially when the flagrum blows started raining down on his back? Maybe he was just whacko. Insane asylums are populated with hundreds of “messiahs”. If that were the case, would he keep it up through the trial, scourging, crowning with thorns, and crucifixion? And what about the resurrection appearances that his followers report? If insanity is your answer it would have to extend to all the people who saw Jesus alive after he was executed. The only possible answer to the biblical accounts is that Jesus was Who he said He was.
Another poster pointed out that Jesus’ appearance matched hundreds of Old Tesament predictions about the coming of-, the life of-, and the death of the messiah.
Then there is the evidence of the Church itself. It was founded by Jesus with a promise that the “Gates of Hell would not prevail”. What other human dynasty, government, organization, or heirarchy has lasted this long? It has outlasted every human institution on Earth despite some of the most despicable people being at all levels of leadership, at one time or another throughout history, perpetrating some of the most evil crimes that humanity has ever known. That alone, in my opinion, is pretty good evidence that God exists and is with the Catholic Church.
But I’ll conclude by repeating that this is a very individual thing. When God touches you, you no longer need proof.