>>513995696
The difference is important because God had made a promise with Abraham's descendants, a contract with mutual obligations. They were to defend and live in the land of Canaan, but after famine and becoming slaves in Egypt they must have lost faith.
God reassured them of this covenant through Moses, many of them died and didn't make it through exodus from Egypt as Moses led them back to their homeland.
Their end of the bargain was that they would be holy men to represent God to the world and be a blessing to every family on Earth. The tribe of Judah(Jews) had broken their end of the deal so they are no longer "chosen for the job".
Instead God chose a few of them through Jesus to carry on the faith, fulfilling prophecy, and becoming a blessing to every family on Earth, Christianity.