In order to say God is unjust for choosing the Israelites, you would have to first answer the question: Chosen for what? People who are unfamiliar with the Bible make the assumption the Israelites were chosen for preferential treatment, and that is not what the Bible says at all. The Bible clearly says that God chose the Israelites to be a “blessing to all the peoples of the world.” Really, he was choosing to send the savior, Jesus, to the world through the Israelites and Jesus came for everyone.
History would tell us that being chosen by God to bless the world was no walk in the park. Lets recall Jewish history:
- Slaves in Egypt
- Wars unending to capture a land, only to lose that land again and again.
- Every time they turn from God they are conquered by enemies.
- Babylonians completely destroy Jerusalem and the temple and take nearly all of the Jews back to Babylon
- Jews return from Babylon, rebuild the city from rubble just to be conquered again by the Romans.
- The Romans eventually destroy the city and the temple again.
- Jewish land isn’t possessed again by the Jews for almost 1900 years.
- Hitler’s concentration camps.
- Stalin’s concentration camps.
If being chosen by God for a duty is unfair, it is unfair to the chosen.
But consider this comparison also. There are literally millions of charities in the world. I personally support about ten. Am I unjust or unfair? Even if I had unlimited resources, am I not allowed to be charitable on whom I want to be charitable, without being considered unfair? How can something be acceptable for a human but unacceptable for God?
Lastly, your question also limits its scope to this human life only, not eternity. If we reconsider that God chose them to bless others, and that they and those they became a blessing for are immortal beings, and we do not know what rewards or punishments await anyone after death, we would be presumptious to declare God unjust based on what we know and see here on earth.