In my studies of the history of Jesus and the Judaism of his times 2 things have stood out recently:
1. Kingdom of God as a saying was only used 4 times in the Tanakh
2. Satan, according to the Jewish Encyclopedia, never appears – and the term ‘the satan’ appears about 4 times in various contexts (namely in Job)
The kingdom of God amount of passages in the NT make sense since the critical times of the era. There was a build-up in messianic fervour and Israel was waiting on a king, like David, to rebuild the kingdom of Israel. Jesus’ focus on this topic fits squarely in with the Judaism of his time.
Satan is a weird concept that gets a lot of play in NT scriptures. The idea is thoroughly not a Hebrew scripture creation and seems to evolve from the Babylonian and Greek ideas. This was allowed fruition under Roman rule since they allowed these ideas to mesh since they accepted outside religious ideas.
Jesus also seemed to cast out demons and heal people afflicted by ‘the satan’. This was a common idea amongst healers of the time, that people were given afflictions by ‘the adversary’ so a healer could cure them.
But all in all, satan was not a focus in the Judaic faith in that age (nor now). So where did this focus come from?
I would contend since Judaism did not focus highly on this concept that the focus was more relatable to the gentile composers of the gospels. Satan was an invention for gentile salvation – which needed zero salvation since they were part of the empire – and it helped create a dualism needed to lift Jesus to salvation for all.