In what way is the Resurrection the best explanation?

[Vicki Q]

According to Bart Ehrman, the suffering servant and resurrection ideas were artifacts of what the disciples observed while also wanting to continue to believe Jesus was the Messiah.

Agreed. No-one expected the Messiah to suffer. However after the Resurrection, they went back to the OT sources like the prophets, with passages such as the suffering servant in Isaiah, and realised the clues had been there all along. I tend to use this as evidence for the resurrection, so I'm a little puzzled here.

Perhaps you should state here what the promise was exactly. You're referring to the Genesis promises to Abraham, aren't you? If so, you'll see that the promise hasn't exactly been delivered if we take a good look at the wording within context.

Things like the Blessing to Humanity, father of many nations, fulfilling the Covenant, sorting out that nasty business in Adam...

I've reread the relevant passages and I'm not sure problems what you're referring to. Remember that Paul and the whole of the (Jewish) Earliest Church were able to claim the promises had been completely fulfilled, so I would think more modern believers should simply follow the same route.

This is also a bit of a mischaracterizing of what I actually suggested in the OP.

Apologies if I've misunderstood. I think therefore it would be helpful for you to flesh out what you are saying. Could you provide a route map from Good Friday to Paul? In particular:

For C1 Jews, the hot topic was the arrival of the Kingdom of God. The internet forums of the day were stuffed with threads about when it was coming, what it would look like, who would be in it etc.

Then there was this rather vague figure of the Messiah (Anointed One) who would bring in the KoG. Anyone claiming to be that was destined to succeed, because God was with them making sure it happened. Therefore, those who failed could not by definition be the Messiah. Their death said, powerfully and irresistibly, this wasn't the Messiah and the KoG hadn't arrived.

That's the theory- it worked like that in practice too. Josephus' writing, Gamaliel's speech in Acts 5, the first and second Jewish rebellions- failure is not an option. Jesus ended up dying exactly like the other failures.

So if the Earliest Church were saying Jesus was the Messiah, he must have succeeded. How?

Fast forward to Paul, writing 20/25 years later. The Resurrection is so well agreed within the Early Church that there is no trace of debate in his letters. Indeed, he uses it as a fixed point from which to deal with the highly disputed issue of Torah obedience.

Paul claims not only that Jesus is the Messiah, but that the Kingdom of God has been inaugurated...Abraham...forgiveness... etc. The reason we know this has happened is because of the Resurrection, he says. And it's clear from his writing that this has been a thing from long before he wrote. All seems to fit together.

So if you could outline your route map it would be helpful. And please point to the evidence for that explanation.