If Jacob and Israel is the same person why does God address them as if they are different people? For example in Isaiah 43:22.
Hebrew is a layered language, which can be hard to understand by those of us that haven’t been trained in it.
One case of this layering is when you find places in the scripture where it seems to repeat itself with only slight alterations. In those cases some additional or reinforcing points were being made in those slight differences. Given that we are using a translation and we aren’t trained in Hebrew it can be easy to miss it or simply not understand.
In the case of the Jacob-Israel combination. Jacob is considered the more worldly or away from God, and Israel is more spiritual and godly. When used together Jacob’s line will have the more negative tone to it. This could be used to compare where they are to where they should be, or a rebuke for the spiritual side for being too worldly.
Of course this is just very brief and simplified answer. There is a lot more research and information in this area that I simply haven’t learned myself.