Tier III
Is Jesus who he said he was?
Two questions: are the Gospels reliable enough to use as historical sources, and what best explains what happened after Jesus' death?
Are the Gospels reliable history?
Judged by the tests historians apply to Tacitus or Josephus, the Gospels and Acts come from the first century, are rooted in the names, places and politics of Jesus' Palestine, and were copied with unusual care: serious historical sources, though not flawless transcripts.
Did Jesus rise from the dead?
The earliest evidence, Paul’s own letters, shows that Jesus’ followers, his sceptical brother and a persecutor all sincerely claimed within a few years to have seen him raised. No natural explanation fits all of it comfortably, so whether you should believe he rose depends mostly on whether you already have reason to think God exists.
The Gospels and Acts come out as early, Palestine-rooted, carefully copied testimony: about eight times more expected that way than as late legend (range 1.2 to 80), which makes them serious historical sources but cannot by itself carry a miracle. It is not evidence that the evangelists never shaped a detail to fit Scripture. The resurrection is the hinge of the whole case. The data from Paul's own letters are secure, and the best natural explanation, grief visions with apocalyptic interpretation, fits them much less well than the claim that God raised Jesus: a likelihood ratio of about 500 (range 1 to 20,000), if the judgements behind it are independent, and about 70 to 450 if they move together.
Since prophecy, scored whole, gives no margin, this tier now carries almost all of the weight that is specific to Christianity: remove the resurrection and Christianity falls from 68.4% to 2.5% from even odds. Even granted in full, the resurrection evidence does far less for the existence of God than for the event, because it can raise the odds of God only as far as God was likely to do this (the limit). Whether it is enough therefore depends on how likely you think it is that God exists at all, which is why Tier III is read together with Tier I in the unified argument.