you made an incorrect assumption, i used to think it was like that too when i started delving into theology. jews are not "chosen" for anything other than conversion to christianity under that god, jesus is quoted having said that his entire purpose was to convert all hebrews to christianity to the point he would even pass up gentiles seeking salvation as well. the son of god had a pretty one track mind but eventually did allow gentiles who showed promise to convert, they just weren't his focus. jews do not have a mandate of heaven, they were mandated by heaven to drop their worship of heathen gods/demons, those who failed to convert in the time of jesus's resurrection and final miracles were told that if they ever left canaan they would break the new covenant.   the old covenant never ended, the new covenant is an addendum not a replacement. the whole point of the new one was that people had to seek him of their own will from then-on, he was never going to personally come save anyone again until the last days. if the old covenant was about showing the miracle to convert, the new one is a period of proving faith and will but most will fail that test.
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