Question:Why did God choose the Israelites as His people? They were the only saved people before the death of Jesus Christ. What about others? Why did God has chosen only Israel as His own people?
"For you are a holy people to the LORD your God; the LORD your God has chosen you to be a people for Himself, a special treasure above all the peoples on the face of the earth. The LORD did not set His love on you nor choose you because you were more in number than any other people, for you were the least of all peoples; but because the LORD loves you, and because He would keep the oath which He swore to your fathers, the LORD has brought you out with a mighty hand, and redeemed you from the house of bondage, from the hand of Pharaoh king of Egypt. Therefore know that the LORD your God, He is God, the faithful God who keeps covenant and mercy for a thousand generations with those who love Him and keep His commandments" (Deuteronomy 7:6-9).
There wasn't anything particular about the Israelites which caused God to pick them as His chosen people. A big part of the reason they were pick was because God made a promise to Abraham and He keeps His promises.
"Do not think in your heart, after the LORD your God has cast them out before you, saying, 'Because of my righteousness the LORD has brought me in to possess this land'; but it is because of the wickedness of these nations that the LORD is driving them out from before you. It is not because of your righteousness or the uprightness of your heart that you go in to possess their land, but because of the wickedness of these nations that the LORD your God drives them out from before you, and that He may fulfill the word which the LORD swore to your fathers, to Abraham, Isaac, and Jacob" (Deuteronomy 9:4-5).
There really wasn't anything particularly attractive about the Israelites. They were given the land of Canaan because the nations which occupied it before them were evil, not because the Israelites were righteous. The truth was that God found dealing with the Israelites a burden. "Furthermore the LORD spoke to me, saying, 'I have seen this people, and indeed they are a stiff-necked people'" (Deuteronomy 9:13). The only reason they survived in the wilderness is because Moses intervened on their behalf.
After reviewing Israel's history, Stephen concluded, "You stiffnecked and uncircumcised in heart and ears! You always resist the Holy Spirit; as your fathers did, so do you. Which of the prophets did your fathers not persecute? And they killed those who foretold the coming of the Just One, of whom you now have become the betrayers and murderers, who have received the law by the direction of angels and have not kept it" (Acts 7:51-53).
In other words, being an Israelite did not save them. There were Israelites who were saved, but they were a relatively small number out of the nation. The nation of Israel did not truly come to being until their acceptance of the covenant with God at Mount Sinai. But there were numerous righteous people before them: Enoch, Noah, Job, Melchizedek, and even Abraham and Isaac. The later two were ancestors of the Israelites, but they were not Israelites -- a point that Paul said was significant:
"And he received the sign of circumcision, a seal of the righteousness of the faith which he had while still uncircumcised, that he might be the father of all those who believe, though they are uncircumcised, that righteousness might be imputed to them also, and the father of circumcision to those who not only are of the circumcision, but who also walk in the steps of the faith which our father Abraham had while still uncircumcised. For the promise that he would be the heir of the world was not to Abraham or to his seed through the law, but through the righteousness of faith. For if those who are of the law are heirs, faith is made void and the promise made of no effect, because the law brings about wrath; for where there is no law there is no transgression. Therefore it is of faith that it might be according to grace, so that the promise might be sure to all the seed, not only to those who are of the law, but also to those who are of the faith of Abraham, who is the father of us all" (Romans 4:11-16).
It should be noted that Cornelius was called a righteous man by God, yet he wasn't an Israelite. "There was a certain man in Caesarea called Cornelius, a centurion of what was called the Italian Regiment, a devout man and one who feared God with all his household, who gave alms generously to the people, and prayed to God always" (Acts 10:1-2). The Israelites did not have exclusive possession of righteousness or God's favor.
Paul also pointed out: "For as many as have sinned without law will also perish without law, and as many as have sinned in the law will be judged by the law (for not the hearers of the law are just in the sight of God, but the doers of the law will be justified; for when Gentiles, who do not have the law, by nature do the things in the law, these, although not having the law, are a law to themselves, who show the work of the law written in their hearts, their conscience also bearing witness, and between themselves their thoughts accusing or else excusing them) in the day when God will judge the secrets of men by Jesus Christ, according to my gospel" (Romans 2:12-16). In other words, it was technically possible for people to live righteously before God even though they weren't Israelites.
What Paul proves in Romans 1-3 is that no one could be saved, whether Jew or Gentile because they all failed to keep God's law "for all have sinned and fall short of the glory of God" (Romans 3:23). That is why Jesus had to step in and why the Law of Moses had to be replaced. Those measures not only aid us toward salvation, but they also reached back to help those who lived before Christ. "And for this reason He is the Mediator of the new covenant, by means of death, for the redemption of the transgressions under the first covenant, that those who are called may receive the promise of the eternal inheritance" (Hebrews 9:15). That should not be taken that everyone under the Old Law were automatically saved by Jesus' death. Rather that Jesus' death allowed God to be merciful to those who basically lived righteously though they had failed from time to time. Nor should you read that as being exclusive only to the Israelites. The Letter of Hebrews was written to the Israelites, so the focus was on their situation, but others benefited from Jesus' death as the chapter of faith (Hebrews 11) demonstrates.