"Chosen before the foundation of the world"

Scripture identifies Israel as those whom God chose before the foundation of the world, the rest of us need to be grafted in.
Deuteronomy 7:6-8 For you are a people holy to the Lord your God. The Lord your God has chosen you to be a people for his treasured possession, out of all the peoples who are on the face of the earth. It was not because you were more in number than any other people that the Lord set his love on you and chose you, for you were the fewest of all peoples, but it is because the Lord loves you and is keeping the oath that he swore to your fathers, that the Lord has brought you out with a mighty hand and redeemed you from the house of slavery, from the hand of Pharaoh king of Egypt.

Israel are the chosen people of God, we as Gentiles need to be grafted in through Messiah.

Ephesians 2:11-13 Don’t forget that you Gentiles used to be outsiders. You were called “uncircumcised heathens” by the Jews, who were proud of their circumcision, even though it affected only their bodies and not their hearts. In those days you were living apart from Christ. You were excluded from citizenship among the people of Israel, and you did not know the covenant promises God had made to them. You lived in this world without God and without hope. But now you have been united with Christ Jesus. Once you were far away from God, but now you have been brought near to him through the blood of Christ.

God's chosen people are not to participate in idolatry or anything that has to do with pagan rituals and beliefs.

Deuteronomy 7:5-6 So then, tear down their altars, break their sacred stone pillars in pieces, cut down their symbols of the goddess Asherah, and burn their idols. Do this because you belong to the Lord your God. From all the peoples on earth he chose you to be his own special people.
Even though Israel was God's chosen people, they got involved with a very popular pagan ritual of sun worship, even right within the LORD's house, which was a great abomination of God.
Ezekiel 8:15-16 Then He said to me, “Have you seen this, O son of man? Turn again, you will see greater abominations than these.” So He brought me into the inner court of the Lord’s house; and there, at the door of the temple of the Lord, between the porch and the altar, were about twenty-five men with their backs toward the temple of the Lord and their faces toward the east, and they were worshiping the sun toward the east.
Today's modern terms used for the same old pagan beliefs and practices that are associated with sun worship is Christmas, Easter, Good Friday, Sunday worship, just to name a few.
In Roman culture, Sunday was the day of the Sun god. In paganism, the Sun was a source of life, giving warmth and illumination to mankind. Sunday - Wikipedia

December 25th was observed as the birthday of the sun as part of the ancient Roman festival called Saturnalia. It was also the date of the birthday of the pagan sun-god Mithras (sometimes also spelled Mithra). {The Catholic Encyclopedia}​

Israel was chosen to be God's representative, to roll out His plan of salvation. They were to be the very people who would bring forth the Messiah.
Micah 5:2 “Bethlehem Ephrathah, you are too little to be among the family groups of Judah. But from you One will come who will rule for Me in Israel. His coming was planned long ago, from the beginning.”
John 4:22 You Samaritans know very little about the one you worship, while we Jews know all about him, for salvation comes through the Jews.
God chose Israel from before the foundation of the world to roll out His plan of salvation, including bringing forth the Messiah, who would ultimately be the Savior of the world. We, as the other nations, benefit from God's plan to save the world through Israel, but we must be grafted into the same plan, and become a coworker of the plan.
Romans 11:11-12 I say then, have they stumbled that they should fall? Certainly not! But through their fall, to provoke Israel to jealousy, salvation has come to the Gentiles.
We provoke Israel to jealousy by obeying God the way Israel was supposed to obey God. This means saying no to all the pagan beliefs and practices of today's mainline churches, and saying yes to God's holy ways. We are to be holy, just as God is holy.
1 Peter 1:13-16 So, prepare your minds for action and exercise self-control. Put all your hope in the gracious salvation that will come to you when Jesus Christ is revealed to the world. So you must live as God’s obedient children. Don’t slip back into your old ways of living to satisfy your own desires. You didn’t know any better then. But now you must be holy in everything you do, just as God who chose you is holy. For the Scriptures say, “You must be holy because I am holy.”
Practicing pagan rituals and beliefs would never provoke Israel to jealousy, because God Israel not to worship Him the way the pagans worship their false gods.
Deuteronomy 12:29-31 When the Lord your God goes ahead of you and destroys the nations and you drive them out and live in their land, do not fall into the trap of following their customs and worshiping their gods. Do not inquire about their gods, saying, ‘How do these nations worship their gods? I want to follow their example.’ You must not worship the Lord your God the way the other nations worship their gods, for they perform for their gods every detestable act that the Lord hates.​

Practically everything Protestants regard as essential or important they have received from the Catholic Church... The Protestant mind does not seem to realize that in accepting the Bible and observing the Sunday, in keeping Christmas and Easter, they are accepting the authority of the spokesman for the church, the Pope. ~ Our Sunday Visitor (February 5, 1950)

The Easter or Ishtar symbolism of the Sunday resurrection of the spring fertility cult (Easter, the Anglo-Saxon form of Ishtar), is a pagan system of worship that first penetrated Christianity in the second century. The symbolism stems from the death of Tammuz on Friday and his resurrection on Sunday. The 40 days of Lent were picked as one day for each year of his life since he died at age 40. The rest of the traditions of Easter were "Christianized" into the story of the death and resurrection of Yeshua the Messiah. "{WikiBooks & Wikipedia}

God's plan is a protected plan, which means, it's going to happen just as God said it would. This means that, even though Israel is God’s chosen people, they have to cooperate with the plan, or they could be cut off, just like those who were grafted in can be cut off.
Romans 11:16-25 For if the first fruit is holy, the lump is also holy; and if the root is holy, so are the branches. And if some of the branches were broken off, and you, being a wild olive tree, were grafted in among them, and with them became a partaker of the root and fatness of the olive tree, do not boast against the branches. But if you do boast, remember that you do not support the root, but the root supports you. You will say then, “Branches were broken off that I might be grafted in.” Well said. Because of unbelief they were broken off, and you stand by faith. Do not be haughty, but fear. For if God did not spare the natural branches, He may not spare you either. Therefore consider the goodness and severity of God: on those who fell, severity; but toward you, goodness, if you continue in His goodness. Otherwise you also will be cut off. And they also, if they do not continue in unbelief, will be grafted in, for God is able to graft them in again. For if you were cut out of the olive tree which is wild by nature, and were grafted contrary to nature into a cultivated olive tree, how much more will these, who are natural branches, be grafted into their own olive tree? For I do not desire, brethren, that you should be ignorant of this mystery, lest you should be wise in your own opinion, that blindness in part has happened to Israel until the fullness of the Gentiles has come in.
Remember, it ain’t over until you hear, “Well done my good and faithful servant.”
Amen...