Why should I believe the resurrection when I wasn't there?

You weren't there for any ancient historical event. That's true of everything from Julius Caesar's assassination to the founding of most nations. Historians still reach real conclusions about the past using sources, corroboration, and careful reasoning—not firsthand presence.

Applied to the resurrection, a small set of facts is accepted by a genuinely wide range of scholars, including skeptical ones: Jesus was executed by crucifixion, his early followers sincerely believed they saw him alive afterward, and at least two people—Paul and James—converted from opposition or skepticism, not gradual persuasion.

Historians disagree on what best explains those facts. Alternative theories exist: hallucination, a faked or mistaken death, later legendary growth. None of them has become the accepted consensus explanation either.

Historical method can weigh the evidence and the competing explanations. Whether a resurrection is even a possible explanation is a further, philosophical question historical method alone doesn't settle. Both the evidence and that deeper question deserve honest attention, not an assumption made in advance.