For one reason, Jesus had to come from some natural line of blood, as all men do, which is why He came from a people, but, for a few reasons, specifically, God chose the Israelites for this because they were descendants of the faithful Abraham, and from their culture that would be established from this lineage, they were then intended to understand the concepts of sin and holiness, and to worship God and follow Him as Abraham did. Therefore, in the long-term, they would make for the best option for a people that Jesus could come from because of this bloodline from Abraham. In addition, yes, another reason would be that their constant turning-aways from God allow us to better comprehend what God wants from us and how we can remain faithful to God.