In a civilised society with justice as its primary goal, testimony obtained under torture is considered invalid. This is because when torture is applied, most people will sing any song their torturer wants in order to escape. Through adequate means of torture, you can make even the strongest people deny what they believe to be true, or even outright lie.
This basic concept, which I'm sure most people will acknowledge, gives us a great evidence for the Gospel. See, although people will usually crack under torture, if they don't, this indicates sincerity. What possible motive would one have to knowingly lie when they could tell the truth and gain their freedom? Yet, the early Church was subjected to extreme persecution, including the theft of property, physical violence, and even death, but there is no evidence any of them recanted.
There is a question mark next to the alleged martyrdom of some of the Apostles. Tradition holds that, of all the Apostles, only John escaped martyrdom, and for most of the Apostles, we might even know how they died. But it is also possible that some of these traditions are not true, and indeed we know at least some of them must be false. Regardless of how exactly each of these people died, it is so indisputable that they all suffered for their faith that no serious historian doubts it. Yet, once again, none of them recanted. Not even one.
Now, make no mistake: no one is saying "they suffered, therefore Christianity is true". The argument is that suffering shows sincerity, not that it shows truth. However, it is an indication of truth in the case of the Apostles because, unlike someone living in 2021, the Apostles, and indeed most of the early Church, were in a position to know if these things were true. In 1 Corinthians 15:6, which was written fairly early on (no later than 60 A.D.), Paul even had the guts to claim "After that He was seen by over five hundred brethren at once, of whom the greater part remain to the present, but some have fallen asleep."
All of this means that, rather than dying for something they just happen to have been taught, these people were dying for things they believed they saw. They saw Jesus, in person, doing His miracles, teaching His sermons, hanging on the cross, and walking around, even eating, after His death. They saw it all, and yet in spite of all the beatings, in spite of all the threats, in spite of the fact they could have gained all kinds of earthly fame by just saying "yeah, you know what, we lied", they were willing to go to their deaths professing Christ, and Him crucified. Now, I don't know about you, but if 12 Apostles, among many others, were willing to die for their consistent testimony, I'm inclined to believe something happened that made them feel that way. The most logical explanation is simply that Christianity is true. Every other conclusion requires far too many unreasonable, usually ad hoc assumptions.
This is very good news, because Christianity goes far beyond just that Christ was crucified and rose again on the third day. What matters is why. First, why was Christ crucified? Of course there is the simple historical context. He offended people to the point they wanted Him dead, so they killed Him. But more important is that He died for us. Every single one of us has offended God by rebelling against Him, which His laws declare requires death. Thus, Christ, who never sinned, died on our behalf. In rising again, He secured eternal life, but only for those who believe. If you confess Jesus as Lord, and believe He rose from the dead, you will be saved.