One criticism of the Bible is that it is just one source, and allegedly the only source that mentions a multitude of Biblical events, most notably the life, death and resurrection of Jesus. Thus, it would be circular reasoning to appeal to the Bible, and the Bible itself is just not evidence.
First, it is worth noting that the Bible is not the only source for a lot of Biblical events. In fact, ironically, there have been times when it lost that title. My go-to example would be the Hittites. The Hittites disappeared from history for a very long time. In the 1800s, one criticism of the Bible was that it must have made them up, because it was seen as unfathomable that an entire culture could just vanish like that. That is until 1903, when the Hittite capital city was re-discovered, and with it, a lot of information about the Hittites. This actually reverses the argument. Where once unbelievers could argue "the Bible is the only source, therefore it must have made it up", Christians can now argue "if the entire Hittite culture could disappear, who knows what other biblical things could be waiting to be recovered?"
But that isn't the point of this article. Rather, I wanted to point out that it is silly to say the Bible is the only source for a given thing, because the Bible is, in fact, not one source. Rather, it is a collection of 66* historical writings. Several of these documents overlap, most notably the Gospels, meaning that actually, we have several independent sources within the Bible.
As I mentioned the Gospels, let's take them as an example. The Gospels overlap in several areas. Each give a selection of accounts, especially of the crucifixion and the resurrection. Some conspiracy theorists even believe there is a mythical document, known as Q, from which all three authors of the first 3 Gospels copied. Of course, this story goes out the window when they want to claim the Gospels contradict each other, but we'll save the hypocrisy of Bible critics for another time. Suffice to say for now, all four Gospels are independent, well witnessed testimony.
So, rather than having just one source for Jesus' crucifixion, we actually have four. Two of these were by eyewitnesses: Matthew, a disciple of Jesus, and John, also a disciple of Jesus, but who was actually at the foot of the cross, so close that Jesus was able to entrust His mother to his care. Another of the Gospels was written by a medical doctor and a historian, who sought to carefully investigate the events and compile his own account for a man named Theophilus. According to that same verse, many had attempted to do so, meaning the Gospels weren't even the only accounts floating around at the time. Finally, Mark, while he wasn't present during the events he records, was a close associate of Peter, who may have even had a strong influence on Mark's gospel.
So, there we have 4 highly qualified contemporaries, who also had help from other eyewitnesses, all testifying to the same things. So, even if we were to ignore the other sources, including hostile witnesses, we have a rather solid historical record of Christ's life, death, and resurrection. We're not just talking about one book that may or may not be of some historical interest. We're talking about a reliable testimony that would hold up in court. Evidence that is, in fact, stronger than what we have for many other historical events that few people deny.
So why do people deny Jesus? Well, it's because they have a rather obvious motive to do so. For 6,000 years, man and God have been at war. God created man and gave us commands, we decided to break those commands and try to dethrone Him. Jesus' trip to the Earth wasn't a social call. It was a rescue mission. In His death, He purchased the forgiveness of sin for all who will believe. But the problem with that is it requires repentance, which isn't easy. As humans, we prefer sin over a relationship with God. Even a restored relationship with Him. That's why some are more willing to believe aliens built the pyramids than that Jesus rose from the dead.
But perhaps the idea of forgiveness is appealing to you. After all, no one wants to be punished, even when they deserve it. When that punishment is eternity in a lake of fire, it becomes even less desirable. But thankfully, God doesn't desire it either, and so He's given us a way out. Believe in the Lord Jesus Christ, and you will be saved.
*This depends on how you divide them. Some Old Testament books, such as 1 and 2 Chronicles, are actually just one book split into two. Thus, if we divide them the Jewish way, it is less than 66.