Despite the fact that Jesus aimed his ministry at the Jewish people, why do you think that the vast majority of Jews refused to convert? And also, the church credits St Paul a lot for it, but why do you think so many gentiles converted? And just to be clear, this post is not meant to challenge people's religious beliefs or assume which religion is right. It's just interesting. Will also post on r/askanthropology since they might have more answers on the cultural aspects.
Despite the fact that Jesus aimed his ministry at the Jewish people, why do you think that the vast majority of Jews refused to convert?
Well Jesus was one of many people claiming to be the Jewish Messiah in the Roman Second Temple period, he wasn't the first and he wasn't the last.
Likewise most of Jesus's teachings weren't all to original or unique to him so really a better question is why would the Jews of his period wish to view him as the Messiah? Some clearly did but most didn't that's just that.
The Church credits St Paul a lot for it, but why do you think so many gentiles converted?
A better question honestly, well early Christianity was was well suited to exploiting the God-Fearer community of the Roman Empire, essentially Paul argued that Gentiles didn't have to keep the Mosaic law if they accepted Jesus, whilst Jews did, so for most Jews there wasn't a big incentive in those days to convert but for your average God-Fearer this probably sounded like a good deal.
Also the Church quite early on decided to use the Septuagint as their standard for the Hebrew Bible, this helped make early Christianity spread earlier amongst the Greek speaking population of Rome.